- Synthesis of Phenols: Organophotoredox/Nickel Dual Catalytic Hydroxylation of Aryl Halides with Water
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A highly effective hydroxylation reaction of aryl halides with water under synergistic organophotoredox and nickel catalysis is reported. The OH group of the resulting phenols originates from water, following deprotonation facilitated by an intramolecular base group on the ligand. Significantly, aryl bromides as well as less reactive aryl chlorides served as effective substrates to afford phenols with a wide range of functional groups. Without the need for a strong inorganic base or an expensive noble-metal catalyst, this process can be applied to the efficient preparation of diverse phenols and enables the hydroxylation of multifunctional pharmaceutically relevant aryl halides.
- Yang, Liu,Huang, Zhiyan,Li, Gang,Zhang, Wei,Cao, Rui,Wang, Chao,Xiao, Jianliang,Xue, Dong
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- Synthesis of Ti-Al binary oxides and their catalytic application for C-H halogenation of phenols, aldehydes and ketones
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Traditional C–H halogenation of organic compounds often requires corrosive agent or harsh condition, and current researches are focused on the use of noble metals as catalyst. In order to give an efficient, benign, activity-adjustable and cost-effective system for halogenation, a series of Ti-Al mixed oxides are prepared as catalyst through sol-gel in this work. Characterizations reveal all catalysts contain more aluminum than titanium, but preparative conditions affect their composition and crystallinity. Monitoring of particle size, zeta potential and UV–vis of preparative solution reveals that formation of catalyst colloids undergoes chemical reaction, affecting catalyst morphology. In halogenation, all catalysts show moderate to high activities, copper chloride proves to be an effective halogen source rather than sodium chloride. The chlorination and bromination are better than iodization, phenol and ketone appear to be more appropriate substrates than aldehyde. Additionally, oxide backbone of catalyst is more durable than its organic components during recycling. This study may provide new catalytic materials for progress of C–H activation.
- Su, Peigen,Fan, Chao,Yu, Heng,Wang, Wanqin,Jia, Xin,Rao, Qifan,Fu, Chenxi,Zhang, Donghua,Huang, Benhua,Pan, Cheng,Zheng, Aqun,Sun, Yang
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- Untersuchungen zur H-Brueckenassoziation von Azaaromaten mit OH-Bruecken-II. H-Brueckenassoziationgleichgewichte von 1,2,7,8-Dibenzacridin mit verschiedenen OH-Donatoren: Ein Vergleich ir-Spektroskopischer und uv-vis-Spektroskopischer Messungen
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The equilibrium of association of 1,2,7,8-dibenzacridine with 7 different OH-donors was investigated in CCl4 as solvent.The results show, that the values measured by infrared spectroscopy as well as by uv-vis-spectroscopy are identical within the respective accuracy limits.
- Juffernbruch, J.,Perkampus, H.-H.
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- Robust and electron deficient oxidovanadium(iv) porphyrin catalysts for selective epoxidation and oxidative bromination reactions in aqueous media
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meso-Tetrakis(3,5-dimethoxyphenyl)porphyrinatooxidovanadium (1) and β-octabromo-meso-tetrakis(2,6-dibromo-3,5-dimethoxyphenyl)porphyrinatooxidovanadium (2) were synthesized in excellent yields. The synthesized oxidovanadium(iv) porphyrin complexes were characterized by various spectroscopic methods such as UV-Vis, FT-IR, EPR and MALDI-TOF mass spectrometry, as well as by single crystal X-ray crystallography. The acetonitrile coordinated porphyrin 1 is relatively planar whereas 2 is highly nonplanar as shown by their crystal structures and also by electrochemical studies. Selective epoxidation studies of alkenes were successfully carried out in CH3CN/H2O as the solvent mixture at ambient temperature resulting in very high TOF numbers (12227-14347 h-1 for 2) even with low catalyst loadings. Remarkably, 2 biomimics the vanadium bromoperoxidase (VBrPO) enzyme with extremely high TOF values (83333-87719 h-1) for the oxidative bromination of thymol and some other phenols. Both the catalysts were successfully recovered at the end of the reactions, indicating their viability and industrial applicability.
- Dar, Tawseef Ahmad,Uprety, Bhawna,Sankar, Muniappan,Maurya, Mannar R.
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- Flavin-Dependent Halogenases from Xanthomonas campestris pv. campestris B100 Prefer Bromination over Chlorination
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Flavin-dependent halogenases selectively introduce halogen substituents into (hetero-)aromatic substrates and require only molecular oxygen and halide salts for this regioselective oxidative CH-functionalization. Genomic analysis of Xanthomonas campestris pv. campestris B100 identified three novel putative members of this enzyme class. They were shown to introduce halogen substituents into, e. g., substituted indoles, while preferring bromide over chloride. (Figure presented.).
- Ismail, Mohamed,Frese, Marcel,Patschkowski, Thomas,Ortseifen, Vera,Niehaus, Karsten,Sewald, Norbert
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- Palladium-catalyzed suzuki-type self-coupling of arylboronic acids. A mechanistic study
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Symmetrical biaryls are formed from arylboronic acids both under tetrakis(triphenylphosphine)-palladium and under palladium(II) acetate catalysis. The principal mechanistic features of these self-couplings have been determined.
- Moreno-Manas, Marcial,Perez, Montserrat,Pleixats, Roser
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- Ultrasonically assisted halogenation of aromatic compounds using isoquinolinium bound hypervalent chromium and tetrabutylammonium halides in PEG-600 solutions under acid free and solvent-free conditions
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Isoquinolinium bound Cr(VI) reagents like isoquinolinium dichromate (IQDC) and isoquinolinium chlorochromate (IQCC) have been successfully accomplished as efficient reagents for oxidative halogenation of aromatic compounds using tetrabutylammonium halide (TBAX) as halogenating agents in aqueous polyethylene glycol (PEG-600) under acid free conditions. Tetrabutylammonium bromide (TBAB) has been used for bromination and tetrabutylammonium iodide (TBAI) for iodination. The halogenation reactions that occurred smoothly in 2 to 7 h under conventional conditions are accelerated magnificently under sonication with few minutes (25 to 70 min) of reaction time and fairly good yields. The reactions occurred at moderate temperature under mild and environmentally safe conditions with simple work up.
- Sambashiva Rao,Ramesh, Kola,Rajanna,Chakrvarthi
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- Organic hypervalent iodine(III) catalyzed ipso-hydroxylation of aryl- and alkylboronic acids/esters
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An organo-hypervalent iodine(III) catalyzed highly efficient methodology for ipso-hydroxylation of diversely functionalized aryl- and alkylboronic acids/esters has been developed using NaIO4 as a co-oxidant. This protocol is also applicable to N-heterocyclic boronic acids and esters. Further mechanistic studies revealed that the organoboronic acid (an electron demanding moiety) is acting as a nucleophile in the presence of hypervalent iodine for hydroxylation reactions. In summary, this is the first Letter of a generalized route for organic hypervalent iodine(III) catalyzed hydroxylation of organoboronic compounds.
- Chatterjee, Nachiketa,Goswami, Avijit
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- Aerobic oxybromination of phenols catalyzed by sodium nitrite under mild conditions
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An efficient catalytic system for oxybromination of phenols under mild conditions has been developed, which utilizes sodium nitrite as the catalyst, dioxygen or air as the terminal oxidant, aqueous hydrobromic acid or molecular bromine as the bromine resource. From both the atom-economic and environmental points of view, the developed protocol is expected to provide a valuable synthetic method for practical applications in laboratory or industry. Georg Thieme Verlag Stuttgart - New York.
- Xu, Li,Wang, Yong,Wen, Xin,Ding, Chengrong,Zhang, Guofu,Liang, Xinmiao
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- Solar-driven conversion of arylboronic acids to phenols using metal-free heterogeneous photocatalysts
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Solar-driven conversion of arylboronic acids to phenols was achieved by employing graphitic carbon nitride (g-C3N4) as heterogeneous photocatalyst, where [rad]O2? was the main active species. By loading g-C3N4 onto the easy weaving low melting point sheath-core composite polyester fibers (LMPET), g-C3N4-based artificial photosynthetic catalytic fabric (g-C3N4/LMPET) with a large light receiving area was prepared. It displayed the efficient conversion of arylboronic acid and excellent recycling performance. This system offers more possibilities to construct an artificial photosynthetic system with excellent solar-to-chemicals conversion efficiency.
- Xu, Tiefeng,Lu, Wangyang,Wu, Xiao-Feng,Chen, Wenxing
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- Transition metal-catalyzed oxidations. 11 : Para-selective chlorination and bromination of phenols with tert-butyl hydroperoxide and TiX(OiPr)3
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Mononuclear phenols 1-4 are chlorinated or brominated with high para-selectivity and in good yields to the halides 5-11 with the TiXn(OiPr)m/TBHP system (X = Cl or Br). WILEY-VCH Verlag GmbH, 1999.
- Krohn, Karsten,Rieger, Hagen,Steingroever, Klaus,Vinke, Ingeborg
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- Visible-light-promoted aerobic oxidative hydroxylation of arylboronic acids in water by hydrophilic organic semiconductor
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A green and sustainable catalytic system was developed based on perylenediimide (PDI) organic semiconductor for the aerobic oxidative hydroxylation of arylboronic acids in aqueous solution with visible light. By using PDI-SN, a hydrophilic organic semiconductor, which can activate oxygen to produce superoxide radicals in aqueous solution, this reaction proceeds under ambient conditions: water as the solvent and air as the oxidant, giving various phenols as products with high yields. In contrast to methods using organic solvents, this novel process has the potential of green industrial application.
- Yu, Kunyi,Zhang, Hanjie,Sheng, Yuqiang,Zhu, Yongfa
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- A comparative study of the hydrolysis pathways of substituted aryl phosphoramidate versus aryl thiophosphoramidate derivatives of stavudine
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A comparative study of aryl phosphoramidate and aryl thiophosphoramidate derivatives of 2′,3′-didehydro-2′,3′-dideoxythymidine (d4T) was performed. The study focused on the nature of the substituents and the influence of a thiophosphoramidate in the structure of these derivatives. The rate of alkaline hydrolysis of these two types of d4T derivatives indicated that replacement of oxygen with sulfur decreases the rate of hydrolysis by twofold. Additionally, the activation energy (Ea) for the sulfur analogs is comparatively higher than that of the oxygen analogs. Notably, an intermediate was formed in the hydrolysis reaction of the sulfur analogs of d4T that was absent in the case of the oxygen analog, and the tentative structure of the intermediate was proposed based on LC/mass spectroscopy data. Using both HPLC and 31P-NMR techniques, we identified the hydrolysis product of the phosphoramidate derivatives and were able to show in in vitro studies that porcine liver esterase can hydrolyze the methyl ester portion of the phosphoramidate derivatives. Aryl phosphoramidate derivatives of d4T were 1000-fold more active than the corresponding aryl thiophosphoramidate derivatives, indicating that the energy of activation of hydrolysis of these phosphoramidate derivatives plays a significant role in their biological potency.
- Venkatachalam,Yu,Samuel,Qazi,Pendergrass,Uckun
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- Mechanism of the acid-catalyzed hydrolysis of N-acylsulfamates
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The kinetics of hydrolysis of a series of N-acylsulfamate esters p-XC6H4OSO2NHCOR as models for more complex, biologically important compounds has been examined. Structure-reactivity, solvent-reactivity, thermodynamic data, etc. support a bimolecular mechanism involving water in the transition state (TS).
- Spillane, William J.,Malaubier, Jean-Baptiste
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- Rongalite-promoted metal-free aerobic ipso-hydroxylation of arylboronic acids under sunlight: DFT mechanistic studies
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A novel rongalite-promoted metal-free aerobic ipso-hydroxylation of arylboronic acids has been developed. This method employs low-cost rongalite as a radical initiator and O2 as a green oxidizing agent for ipso-hydroxylation. This protocol is compatible with a wide variety of functional groups with good to excellent yields at room temperature. Furthermore, mechanistic insight into the role of superoxide radical anions in C-B cleavage has also been provided based on DFT studies.
- Golla, Sivaparwathi,Poshala, Soumya,Pawar, Ravinder,Kokatla, Hari Prasad
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- Boronic ester as a linker system for solid phase synthesis
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A method for attaching boronic acids to a macroporous polymer-supported 1,3-diol was developed. Chemical modifications of some polymer-bound arylboronic acids were realised using various reaction conditions. Trans-esterification gave new boronates in high purity while oxidative cleavage directly led to phenols.
- Carboni, Bertrand,Pourbaix, Christelle,Carreaux, Francois,Deleuze, Herve,Maillard, Bernard
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- Highly efficient, recyclable and alternative method of synthesizing phenols from phenylboronic acids using non-endangered metal: Samarium oxide
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Oxidation of phenylboronic acid to phenol is one of the important industrial processes and it is generally employed in the plastic, explosive and drug manufacturing industries. Over the past decades, numerous efficient methods have been described for the generation of phenols from phenylboronic acids in the presence of oxidant. However, these methods suffered from various limitations, including the use of expensive, toxic reagents and sophisticated protocol to synthesise the phenols. Additionally, some of these reported literatures employed endangered metals, in which mankind is facing the risk of limited supply of these elements in 20 years’ time from now. As such, a viable alternative and green method for achieving organic synthesis is highly sought after by the chemists of today. Herein, we report for the first time a facile, efficient and alternative method in the preparation of phenols from phenylboronic acids using non-endangered metal as catalyst. In all cases, all phenols were afforded in satisfactory yields (81–96%) by employing column-free method. In the recyclability study, the Sm2O3 catalyst was found to possess good catalytic performance, even after being reused for five consecutive times (96–91%). In addition, SEM result revealed that the morphology of the recycled Sm2O3 catalyst was well preserved after five successive uses, which indicate no observable changes occurred in the recovered catalysts. As a final note, the current method is anticipated to be useful for industries manufacturing chemical intermediates as it provides an alternative method of catalysis by using a non-endangered metal in organic transformations.
- Yusoff, Hanis Mohd,Bala Chandran, Prasana Devi,Sayuti, Fatin Amira Binti,Kan, Su-Yin,Mohd Radzi, Siti Aisha,Yong, Fu-Siong Julius,Lee, Oon Jew,Chia, Poh Wai
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- An efficient method for demethylation of aryl methyl ethers
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A new efficient method for demethylation of aryl methyl ethers using iodocyclohexane in DMF under reflux condition is described.
- Zuo, Li,Yao, Shanyan,Wang, Wei,Duan, Wenhu
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- The Catalyst-Controlled Regiodivergent Chlorination of Phenols
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Different catalysts are demonstrated to overcome or augment a substrate's innate regioselectivity. Nagasawa's bis-thiourea catalyst was found to overcome the innate para-selectivity of electrophilic phenol chlorination, yielding ortho-chlorinated phenols that are not readily obtainable via canonical electrophilic chlorinations. Conversely, a phosphine sulfide derived from 2,2′-Bis(diphenylphosphino)-1,1′-binaphthyl (BINAP) was found to enhance the innate para-preference of phenol chlorination.
- Maddox, Sean M.,Dinh, Andrew N.,Armenta, Felipe,Um, Joann,Gustafson, Jeffrey L.
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- Directed Structural Transformations of Coordination Polymers Supported Single-Site Cu(II) Catalysts to Control the Site Selectivity of C-H Halogenation
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A main difficulty in C-H bond functionalization is to undertake the catalyst control accurately where the reaction takes place. In this work, to achieve highly effective and regioselective single-site catalysts, a three-dimensional (3D) rhombus-like framework of {[Mn(Hidbt)DMF]·H2O}n (1) [H3idbt = 5,5′-(1H-imidazole-4,5-diyl)-bis(2H-tetrazole)] containing coordinated DMF molecules was constructed. For the dissolution-recrystallization structural transformation process, attractive structural transformations proceeded from 1 to a new crystalline species formulated as {[Mn3(idbt)2(H2O)2]·3H2O}n (2) with a 3D windowlike architecture, and then the Mn ions in 2 could be exchanged with Cu ions through cation exchange in a single-crystal to single-crystal fashion to produce the Cu-exchanged product {[Mn2Cu(idbt)2(H2O)2]·3H2O}n (2a), which had a windowlike framework like that of 2. Furthermore, 2 and 2a were used as heterogeneous catalysts for the regioselective C-H halogenation of phenols with N-halosuccinimides (NCS and NBS) to produce the site selective single monohalogenated products. It was found that the catalytic activity and site selectivity of 2a were much higher than those of 2, because the unique structural features of 2a with the uniformly dispersed CuII active centers served as a single-site catalyst with a site-isolated and well-defined platform to promote the C-H halogenation reaction in regiocontrol and guide an orientation that favored the para selectivity during the reaction process.
- Huang, Chao,Zhu, Kaifang,Zhang, Yingying,Shao, Zhichao,Wang, Dandan,Mi, Liwei,Hou, Hongwei
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- Accelerated Discovery in Photocatalysis using a Mechanism-Based Screening Method
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Herein, we report a conceptually novel mechanism-based screening approach to accelerate discovery in photocatalysis. In contrast to most screening methods, which consider reactions as discrete entities, this approach instead focuses on a single constituent mechanistic step of a catalytic reaction. Using luminescence spectroscopy to investigate the key quenching step in photocatalytic reactions, an initial screen of 100 compounds led to the discovery of two promising substrate classes. Moreover, a second, more focused screen provided mechanistic insights useful in developing proof-of-concept reactions. Overall, this fast and straightforward approach both facilitated the discovery and aided the development of new light-promoted reactions and suggests that mechanism-based screening strategies could become useful tools in the hunt for new reactivity. Enlightened! A mechanism-based screening approach can accelerate discovery in photocatalysis. It focuses on a single mechanistic step of a reaction class: the quenching step central to photocatalytic transformations. Luminescence spectroscopy was used to screen 100 compounds, identifying two promising substrate classes. A second, more-focused screen provided mechanistic insights for developing proof-of-concept reactions.
- Hopkinson, Matthew N.,Gómez-Suárez, Adrián,Teders, Michael,Sahoo, Basudev,Glorius, Frank
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- Vanadium bromoperoxidase (VBrPO) mimics: Synthesis, structure and a comparative account of the catalytic activity of newly synthesized oxidovanadium and oxido-peroxidovanadium complexes
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The bioinspired catalytic activities of two newly synthesised vanadium(iv)dioxido (complex 1) and vanadium(v) oxido-peroxido (complex 2) complexes with the neutral tridentate benzimidazole ligand, 2,6-di-(1H-benzo[d]imidazol-2-yl)pyridine (Byim) have been established. The bromoperoxidase activities of these complexes have been established through the activation of C-H bonds of substrates like phenol, o-cresol and p-cresol. The products, characterized by GC analysis shows that good conversions have been achieved. Considering the catalytic efficiency of the complexes, complex 2, with one in-built peroxido group is found to be more potent than complex 1. The catalytic cycles of both the complexes have been established from experimental results.
- Palmajumder, Eshita,Patra, Swarup,Drew, Michael G. B.,Mukherjea, Kalyan K.
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- A facile and catalytic method for selective deprotection of tert-butyldimethylsilyl ethers with copper(II) bromide
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Copper(II) bromide is found to be a simple and efficient catalyst for selective deprotection of tert-butyldimethylsilyl ethers of alcohols/phenols at ambient temperature. Various labile functional groups such as ketal, alkene, ketone, OTBDPS, OTHP and allyl and benzyl ethers are found to be compatible under the reaction conditions.
- Bhatt, Suchitra,Nayak, Sandip K.
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- Unexpected hydrazine hydrate-mediated aerobic oxidation of aryl/ heteroaryl boronic acids to phenols in ambient air
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The expedient and efficient sub-stoichimetric hydrazine hydrate-mediated aerobic hydroxylation of boronic acids that proceeds in poly(ethylene glycol) (PEG-400) has been successfully developed, providing diverse phenols in high yields. And heteroaryl boronic acids are also amenable to this protocol. the Partner Organisations 2014.
- Zhong, Yanzhen,Yuan, Linxin,Huang, Zheng,Gu, Wenchao,Shao, Ye,Han, Wei
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- Efficient and selective demethylation of heteroaryl methyl ethers in the presence of aryl methyl ethers
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A new and efficient method for the demethylation of 6-membered aza-heterocyclic methyl ethers is described using lithium chloride and para-toluenesulfonic acid. This process is chemoselective for aza-heterocyclic methyl ethers in the presence of aryl methyl ethers.
- Soni, Ajay,Dutt, Akhilesh,Sattigeri, Viswajanani,Cliffe, Ian A.
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- Halogenation Using N-Halogenocompounds. I. Effect of Amines on ortho-Bromination of Phenols with NBS
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Primary and secondary amines, especially diisopropylamine and dibutylamine, catalyzed ortho-dibromination of phenol and ortho-monobromination of 2-substituted phenols with NBS in dichloromethane to give selectively 2,6-dibromophenol and 2-bromo-6-sybstituted phenols, respectively.The effective intermediates are inferred to be N-bromoamines.The scope and limitations of the bromination are also presented.
- Fujisaki, Shizuo,Eguchi, Hisao,Omura, Atsushi,Okamoto, Atsushi,Nishida, Akiko
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- Blacklight-Induced Hydroxylation of Arylboronic Acids Leading to Hydroxyarenes Using Molecular Oxygen and Tetrabutylammonium Borohydride
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A new simple protocol for the conversion of arylboronic acids to hydroxyarenes was achieved using molecular oxygen in the presence of tetrabutylammonium borohydride under blacklight irradiation (360 nm). A radical chain mechanism in which a superoxide ion (O2?.) plays a key role is proposed.
- Kawamoto, Takuji,Ryu, Ilhyong
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- Base-promoted, mild and highly efficient conversion of arylboronic acids into phenols with tert-butyl hydroperoxide
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A mild and efficient protocol for the synthesis of phenols from arylboronic acids has been developed by using tert-butyl hydroperoxide with base as promoter. The corresponding phenols were obtained in good to excellent yields within several minutes. Georg Thieme Verlag Stuttgart New York.
- Guo, Shengmei,Lu, Lin,Cai, Hu
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- Regioselective bromination of arenes mediated by triphosgene-oxidized bromide
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This article first time describes triphosgene (BTC) as an oxidant while the non-toxic and easy-to-handle potassium bromide (KBr) as the source of bromine to the bromination reaction of aromatic substrates. The novel brominating protocol gives excellent para-regioselectivity of the alkoxyl/hydroxyl arenes and high yield, offering good potential of commercial scale applications. The mechanism of “Triphosgene oxidize bromide” was proposed.
- Xu, Yingzhou,Hu, Dufen,Zheng, Hui,Mei, David,Gao, Zhaobo
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- Transformation of diphenyl ethers by Trametes versicolor and characterization of ring cleavage products
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The white-rot fungi Trametes versicolor SBUG 1050, DSM 11269 and DSM 11309 are able to oxidize diphenyl ether and its halogenated derivatives 4- bromo- and 4-chlorodiphenyl ether. The products formed from diphenyl ether were 2- and 4-hydroxydiphenyl ether. Both 4-bromo- and 4-chlorodiphenyl ether were transformed to the corresponding products hydroxylated at the non- halogenated ring. Additionally, ring-cleavage products were detected by high performance liquid chromatography and characterized by gas chromatography/mass spectrometry and proton nuclear magnetic resonance spectroscopy. Unhalogenated diphenyl ether was degraded to 2-hydroxy-4- phenoxymuconic acid and 6-carboxy-4-phenoxy-2-pyrone. Brominated derivatives of both these compounds were formed from 4-bromodiphenyl ether, and 4- chlorodiphenyl ether was transformed in the same way to the analogous chlorinated ring cleavage products. Additionally, 4-bromo- and 4-chlorophenol were detected as intermediates from 4-bromo- and 4-chlorodiphenyl ether, respectively. In the presence of the cytochrome-P450 inhibitor 1- aminobenzotriazole, no metabolites were formed by cells of Trametes versicolor from the diphenyl ethers investigated. Cell-free supernatants of whole cultures with high laccase and manganese peroxidase activities were not able to transform the unhydroxylated diphenyl ethers used. The white-rot fungi Trametes versicolor SBUG 1050, DSM 11269 and DSM 11309 are able to oxidize diphenyl ether and its halogenated derivatives 4-bromo- and 4-chlorodiphenyl ether. The products formed from diphenyl ether were 2- and 4-hydroxydiphenyl ether. Both 4-bromo- and 4-chlorodiphenyl ether were transformed to the corresponding products hydroxylated at the non-halogenated ring. Additionally, ring-cleavage products were detected by high performance liquid chromatography and characterized by gas chromatography/mass spectrometry and proton nuclear magnetic resonance spectroscopy. Unhalogenated diphenyl ether was degraded to 2-hydroxy-4-phenoxymuconic acid and 6-carboxy-4-phenoxy-2-pyrone. Brominated derivatives of both these compounds were formed from 4-bromodiphenyl ether, and 4-chlorodiphenyl ether was transformed in the same way to the analogous chlorinated ring cleavage products. Additionally, 4-bromo- and 4-chlorophenol were detected as intermediates from 4-bromo- and 4-chlorodiphenyl ether, respectively. In the presence of the cytochrome-P450 inhibitor 1-aminobenzotriazole, no metabolites were formed by cells of Trametes versicolor from the diphenyl ethers investigated. Cell-free supernatants of whole cultures with high laccase and manganese peroxidase activities were not able to transform the unhydroxylated diphenyl ethers used.
- Hundt, Kai,Jonas, Ulrike,Hammer, Elke,Schauer, Frieder
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- Observation of Transient Cyclohexadienones during the Aqueous Bromination of Phenols
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Transient 4-bromo-2,5-cyclohexadienone intermediates have been observed during the aqueous bromination of phenol and several methylated derivatives.They enolize to the corresponding p-bromophenols by both acid-catalyzed and water-catalyzed pathways in the pH range 0-6.Studies carried out in buffers also indicate both general acid catalysis (α ca 0.0) and general base catalysis (β=0.54).The latter is ascribed to simple rate-limiting proton abstraction, but the former is not so easily rationalized.The very low α is attributed to a termolecular transition state (water, substrate, and general acid) in which the dienone becomes more anion-like than cation like.This seemingly anomalous behaviour can be explained by the very large enol/keto ratio (ca. 1011) for phenol.
- Tee, Oswald S.,Iyengar, N. Rani
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- Light-Induced Efficient Hydroxylation of Benzene to Phenol by Quinolinium and Polyoxovanadate-Based Supramolecular Catalysts
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Direct Hydroxylation of benzene to phenol with high yield and selectivity has been the goal of phenol industrial production. Photocatalysis can serve as a competitive method to realize the hydroxylation of benzene to phenol owing to its cost-effective and environmental friendliness, however it is still a forbidding challenge to obtain good yield, high selectivity and high atom availability meanwhile. Here we show a series of supramolecular catalysts based on alkoxohexavanadate anions and quinolinium ions for the photocatalytic hydroxylation of benzene to phenol under UV irradiation. We demonstrate that polyoxoalkoxovanadates can serve as efficient catalysts which can not only stabilize quinolinium radicals but also reuse H2O2 produced by quinolinium ions under light irradiation to obtain excellent synergistic effect, including competitive good yield (50.1 %), high selectivity (>99 %) and high atom availability.
- Gu, Yaqi,Huang, Yichao,Li, Qi,Wei, Yongge,Yu, Han,Zang, Dejin
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- A practical highly selective oxybromination of phenols with dioxygen
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A simple, low cost and highly selective method for the synthesis of mono-bromophenols from phenol and electron-rich phenolic compounds has been developed. Bromide ions are used as halogenating agents, dioxygen as a final oxidant, and Cu(OAc)2 as a catalyst.
- Menini, Luciano,Parreira, Luciana A.,Gusevskaya, Elena V.
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- An efficient, rapid, and regioselective bromination of anilines and phenols with 1-butyl-3-methylpyridinium tribromide as a new reagent/solvent under mild conditions
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1-Butyl-3-methylpyridinium tribromide, [BMPy]Br3 proves to be a highly efficient, regioselective reagent/solvent for nuclear bromination of various anilines and phenols. The synthesis and characterization of the room temperature ionic liquid [BMPy]Br3 (2) is described. The bromination was carried out in the absence of organic solvents and in most cases the only extraction solvent needed was water. The spent 1-butyl-3-methylpyridinium bromide (1) was easily recycled.
- Borikar, Sanjay P.,Daniel, Thomas,Paul, Vincent
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- Development of a palladium-catalyzed α-arylation of cyclopropyl nitriles
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1,1-Disubstituted aryl cyclopropyl nitriles are useful moieties in biologically active compounds and provide access to a range of cyclopropyl derivatives. Herein, we describe the development of a palladium-catalyzed α-arylation of cyclopropyl, cyclobutyl, and cyclopentyl nitriles that affords these functional groups in one step from a variety of aryl bromides in good to excellent yields. Furthermore, we demonstrate the transformation of aryl cyclopropyl nitriles into aryl trifluoromethyl cyclopropanes.
- McCabe Dunn, Jamie M.,Kuethe, Jeffrey T.,Orr, Robert K.,Tudge, Matthew,Campeau, Louis-Charles
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- Synthesis, characterization, X-ray crystal structure, DFT calculations, and catalytic properties of a dioxidovanadium(V) complex derived from oxamohydrazide and pyridoxal: A model complex of vanadate-dependent bromoperoxidase
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A vanadium(V) complex with the formula [Et3NH][VVO2(sox-pydx)] with a new tridentate ligand 2-[2-[[3-hydroxy-5-(hydroxymethyl)-2-methylpyridin-4-yl]methylene]hydrazinyl]-2-oxoacetamide (soxH-pydxH), obtained by condensation of oxamohydrazide and pyridoxal (one of the forms of vitamin B6), has been synthesized. The compound was characterized by various analytical and spectroscopic methods, and its structure was determined by single-crystal X-ray diffraction technique. Density functional theory (DFT) and time-dependent DFT calculations were used to understand the electronic structure of the complex and nature of the electronic transitions observed in UV-vis spectra. In the complex, vanadium(V) is found to be pentacoordinated with two oxido ligands and a bianionic tridentate ONO-donor ligand. The vanadium center has square-pyramidal geometry with an axial oxido ligand, and the equatorial positions are occupied by another oxido ligand and a phenolato oxygen, an imine nitrogen, and a deprotonated amide oxygen of the hydrazone ligand. A DFT-optimized structure of the complex shows very similar metrical parameters as determined by X-ray crystallography. The O4N coordination environment of vanadium and the hydrogen-bonding abilities of the pendant amide moiety have a strong resemblance with the vanadium center in bromoperoxidase enzyme. Bromination experiments using H2O2 as the oxidizing agent, with model substrate phenol red, and the vanadium complex as a catalyst show a remarkably high value of kcat equal to 26340 h-1. The vanadium compound also efficiently catalyzes bromination of phenol and salicylaldehyde as well as oxidation of benzene to phenol by H2O2.
- Das, Chandrima,Adak, Piyali,Mondal, Satyajit,Sekiya, Ryo,Kuroda, Reiko,Gorelsky, Serge I.,Chattopadhyay, Shyamal Kumar
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- Molecular cloning, structure, and reactivity of the second bromoperoxidase from Ascophyllum nodosum
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The sequence of bromoperoxidase II from the brown alga Ascophyllum nodosum was determined from a full length cloned cDNA, obtained from a tandem mass spectrometry RT-PCR-approach. The clone encodes a protein composed of 641 amino-acids, which provides a mature 67.4 kDa-bromoperoxidase II-protein (620 amino-acids). Based on 43% sequence homology with the previously characterized bromoperoxidase I from A. nodosum, a tertiary structure was modeled for the bromoperoxidase II. The structural model was refined on the basis of results from gel filtration and vanadate-binding studies, showing that the bromoperoxidase II is a hexameric metalloprotein, which binds 0.5 equivalents of vanadate as cofactor per 67.4 kDa-subunit, for catalyzing oxidation of bromide by hydrogen peroxide in a bi-bi-ping-pong mechanism (kcat = 153 s-1, 22 °C, pH 5.9). Bromide thereby is converted into a bromoelectrophile of reactivity similar to molecular bromine, based on competition kinetic data on phenol bromination and correlation analysis. Reactivity provided by the bromoperoxidase II mimics biosynthesis of methyl 4-bromopyrrole-2-carboxylate, a natural product isolated from the marine sponge Axinella tenuidigitata.
- Wischang, Diana,Radlow, Madlen,Schulz, Heiko,Vilter, Hans,Viehweger, Lutz,Altmeyer, Matthias O.,Kegler, Carsten,Herrmann, Jennifer,Mueller, Rolf,Gaillard, Fanny,Delage, Ludovic,Leblanc, Catherine,Hartung, Jens
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- Continuous-flow hydroxylation of aryl iodides promoted by copper tubing
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A simple and ligand-free synthesis of phenols from the corresponding aryl iodides in a continuous-flow system is described. The reaction is complete in only 4 to 20 minutes when heated between 150 to 165 °C in a reactor consisting of a commercially available copper coil. An example of trapping of the phenoxide in situ is also shown.
- Cyr, Patrick,Charette, André B.
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- Luminescent ruffled iridium(iii) porphyrin complexes containing N-heterocyclic carbene ligands: structures, spectroscopies and potent antitumor activities under dark and light irradiation conditions
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A panel of iridium(iii) porphyrin complexes containing axial N-heterocyclic carbene (NHC) ligand(s) were synthesized and characterized. X-ray crystal structures of the bis-NHC complexes [IrIII(ttp)(IMe)2]+ (2a), [IrIII(oep)(BIMe)2]+ (2d), [IrIII(oep)(IiPr)2]+ (2e) and [IrIII(F20tpp)(IMe)2]+ (2f) display ruffled porphyrin rings with mesocarbon displacements of 0.483-0.594 ? and long Ir-CNHC bonds of 2.100-2.152 ?. Variable-temperature 1H NMR analysis of 2a reveals that the macrocycle porphyrin ring inversion takes place in solution with an activation barrier of 40 ± 1 kJ mol?1. The UV-vis absorption spectra of IrIII(por)-NHC complexes display split Soret bands. TD-DFT calculations and resonance Raman experiments show that the higher-energy Soret band is derived from the 1MLCT dπ(Ir) → π*(por) transition. The near-infrared phosphorescence of IrIII(por)-NHC complexes from the porphyrin-based 3(π, π*) state features broad emission bands at 701-754 nm with low emission quantum yields and short lifetimes (Φem III(por)(IMe)2]+ complexes (por = ttp and oep) are efficient photosensitizers for 1O2 generation (Φso = 0.64 and 0.88) and are catalytically active in the light-induced aerobic oxidation of secondary amines and arylboronic acid. The bis-NHC complexes exhibit potent dark cytotoxicity towards a panel of cancer cells with IC50 values at submicromolar levels. The cytotoxicity of these complexes could be further enhanced upon light irradiation with IC50 values as low as nanomolar levels in association with the light-induced generation of reactive oxygen species (ROS). Bioimaging of [IrIII(oep)(IMe)2]+ (2c) treated cells indicates that this Ir complex mainly targets the endoplasmic reticulum. [IrIII(oep)(IMe)2]+ catalyzes the photoinduced generation of singlet oxygen and triggers protein oxidation, cell cycle arrest, apoptosis and the inhibition of angiogenesis. It also causes pronounced photoinduced inhibition of tumor growth in a mouse model of human cancer.
- Lam, Tsz-Lung,Tong, Ka-Chung,Yang, Chen,Kwong, Wai-Lun,Guan, Xiangguo,Li, Ming-De,Kar-Yan Lo, Vanessa,Lai-Fung Chan, Sharon,Lee Phillips, David,Lok, Chun-Nam,Che, Chi-Ming
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- Untersuchungen zur H-Brueckenassoziation von Azaaromaten mit OH-Bruecken-III. Loesungsmittelabhaengigkeit der Assoziationsgleichgewichte zwischen 1,2,7,8-Dibenzacridin und OH-Donatoren
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The association equilibria of the H-bridges between dibenzacridine (DBA) and 7 different OH-donors were investigated in CCl4, n-heptane, toluene and benzene as solvents by uv-vis spectroscopic methods.The results show a significant dependence of the association constants and the thermodynamic data upon the solvents used.This solvent dependence is thoroughly discussed in connection with the spectroscopic data.
- Juffernbruch, J.,Perkampus, H.-H.
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- Formation and reactivity of 4-oxocyclohexa-2,5-dienylidene in the photolysis of 4-chlorophenol in aqueous solution at ambient temperature
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Nanosecond laser flash photolysis of an aqueous solution of 4-chlorophenol (λexc = 266 nm) produces, at pulse end, a transient with absorption maxima at 384, 370, and ca. 250 nm; upon addition of an H-donor such as 2-propanol, this spectrum is converted into that of the phenoxyl radical (λmax = 400 and 385 nm), and in presence of O2, it is converted into a transient with a broad absorption band peaking at 460 nm. This reaction behavior can be understood by assuming formation of the carbene, 4-oxocyclohexa-2,5-dienylidene, by elimination of HCl from excited 4-chlorophenol; the pulse end transient spectrum is assigned to this species, while the 460 nm band is assigned to benzoquinone O-oxide formed by addition of O2 to the carbene. Both phenoxyl radical and benzoquinone O-oxide are produced upon photolysis of 4-chlorophenol in neat alkanols as well. On the other hand, photolysis in n-hexane yields the triplet-triplet absorption, which is absent in polar solvents, and no indication of carbene formation. It can be concluded that the primary step of 4-chlorophenol photolysis in aqueous or alcoholic solution is heterolytic C-Cl bond scission; a quantum yield of 0.75 is determined for it in neutral or acid aqueous medium upon excitation at 266 nm. Photolysis of chlorophenolate produces the same transients, but with a markedly lower yield, and, in addition, eaq- and 4-chlorophenoxyl radicals. The proposed reaction mechanism provides a straightforward explanation of the results of photoproduct analysis, published by previous authors as well as contributed in the present work. In particular, formation of p-benzoquinone in the presence of O2 can be accounted for by intermediate formation of benzoquinone O-oxide. Production of 4-oxocyclohexa-2,5-dienylidene with high yield allows, for the first time, extensive investigation of the kinetics and mechanism of the reactions of a carbene in an aqueous environment. In the present work, we have studied (a) the addition reaction with O2 on the one hand and with halides on the other; (b) H abstraction reactions with alkanols; (c) reaction with 4-chlorophenol itself; and (d) reaction with H2O. The rate constants for reaction with O2 (3.5 × 109 M-1 s-1) and with I- (4.6 × 109 M-1 s-1) are close to the diffusion-controlled limit, whereas reactions with Br- (6.8 × 107 M-1 s-1) and Cl- (5 M-1 s-1) are slower. Rate constants for reaction with alkanols follow the pattern known for their reactions with radicals, with values ranging from 5 × 105 M-1 s-1 for tert-butyl alcohol to 1.9 × 107 M-1 s-1 for 2-butanol. All these observations are consistent with the triplet character of the carbene. A rate constant of 1.5 × 103 M-1 s-1 has been determined for reaction with H2O. This reaction is not accompanied by formation of OH radicals; it is concluded that it proceeds by insertion into the O-H bond rather than by O-H cleavage. The exceptional stability of the carbene in aqueous solution is thus mainly attributed to the high barrier for O-H rupture in the water molecule. Additionally, a specific carbene-H2O interaction is revealed by semiempirical calculations, which could contribute to energetic and orientational hindrance of the reaction. Further theoretical results support the interpretation of both spectroscopic and kinetic properties of the carbene.
- Grabner, Gottfried,Richard, Claire,K?hler, Gottfried
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- Improved, odorless access to Benzo[1,2-d;4,5-d′]-bis[1,3]dithioles and tert-butyl arylsulfides via C-S cross coupling
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Benzo[1,2-d;4,5-d′]bis[1,3]dithioles are important building blocks within a range of functional materials such as fluorescent dyes, conjugated polymers, and stable trityl radicals. Access to these is usually gained via tert-butyl aryl sulfides, the synthesis of which requires the use of highly malodorous tert-butyl thiol and relies on SNAr-chemistry requiring harsh reaction conditions, while giving low yields. In the present work, S-tert-butyl isothiouronium bromide is successfully applied as an odorless surrogate for tert-butyl thiol. The C-S bond formation is carried out under palladium catalysis with the thiolate formed in situ resulting in high yields of tert-butyl aryl sulfides. The subsequent formation of benzo[1,2-d;4,5-d′]bis[1,3]dithioles is here achieved with scandium(III)triflate, a less harmful reagent than the usually used Lewis acids, e.g., boron trifluoride or tetrafluoroboric acid. This enables a convenient and environmentally more compliant access to high yields of benzo[1,2-d;4,5-d′]bis[1,3]dithioles.
- Fleck, Nico,Kopp, Kevin,Schiemann, Olav
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- C70 Fullerene-Catalyzed Metal-Free Photocatalytic ipso-Hydroxylation of Aryl Boronic Acids: Synthesis of Phenols
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A metal-free C70 fullerene-catalyzed method has been developed for the ipso-hydroxylation of aryl and heteroaryl boronic acids to corresponding phenols under photocatalytic conditions. The reaction proceeds under oxygen atmosphere and the mechanistic study revealed that C70 plays a critical role in the generation of reactive oxygen species in the presence of blue light. Reactions in the presence of 18O-labelled water and oxygen confirmed the generation of reactive oxygen species from oxygen molecule. Amine used as a reductant could be recovered in the form of imine. The current method is also applicable to the synthesis of aryl ethers in one-pot two-step process. (Figure presented.).
- Kumar, Inder,Sharma, Ritika,Kumar, Rakesh,Kumar, Rakesh,Sharma, Upendra
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- Benzoquinone-promoted aerobic oxidative hydroxylation of arylboronic acids in water
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A general and efficient aerobic oxidative hydroxylation of arylboronic acids promoted by benzoquinone in water was realized, and provided phenols in 72-95% yields for 20 examples. The main advantages of this protocol are the use of water as solvent in the presence of a catalytic amount of benzoquinone, and metal-free conditions. Georg Thieme Verlag KG Stuttgart · New York.
- Cheng, Guolin,Zeng, Xiaobao,Cui, Xiuling
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- Imidazolium-urea low transition temperature mixtures for the UHP-promoted oxidation of boron compounds
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Different carboxy-functionalized imidazolium salts have been considered as components of low transition temperature mixtures (LTTMs) in combination with urea. Among them, a novel LTTM based on 1-(methoxycarbonyl)methyl-3-methylimidazolium chloride and urea has been prepared and characterized by differential scanning calorimetry throughout its entire composition range. This LTTM has been employed for the oxidation of boron reagents using urea-hydrogen peroxide adduct (UHP) as the oxidizer, thus avoiding the use of aqueous H2O2, which is dangerous to handle. This metal-free protocol affords the corresponding alcohols in good to quantitative yields in up to 5 mmol scale without the need of further purification. The broad composition range of the LTTM allows for the reaction to be carried out up to three consecutive times with a single imidazolium salt loading offering remarkable sustainability with an E-factor of 7.9, which can be reduced to 3.2 by the threefold reuse of the system.
- Martos, Mario,Pastor, Isidro M.
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- A highly photosensitive covalent organic framework with pyrene skeleton as metal-free catalyst for arylboronic acid hydroxylation
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Covalent organic frameworks (COFs) have been widely utilized in metal-free photocatalytic synthesis base on their excellent properties such as super conjugation, porosity and stability. In this work, we synthesized a new COF material using 1,3,6,8-Tetrakis (p-formylphenyl)pyrene (TFPPy) and 2,2′-Dimethylbenzidine (DMBZ) as basic units through Schiff base condensation reaction. The new COF (TF-DM COF) was applied as metal-free catalyst for hydroxylation of arylboronic acids. The results indicated that the extended π conjugation of COFs enhanced the absorption of visible light, and the large porosity (BET surface area: 113.782 m2g?1) accelerated the reaction rate. Good recyclability enables it with multiple applications, which result in a great reducing of the cost. This study reports that TF-DM COF has a broad application prospect as a new generation of metal-free photocatalysts for organic conversions.
- Chen, Ying,Huo, Jianqiang,Zhang, Yubao
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- Electrophotocatalytic C?H Heterofunctionalization of Arenes
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The electrophotocatalytic heterofunctionalization of arenes is described. Using 2,3-dichloro-5,6-dicyanoquinone (DDQ) under a mild electrochemical potential with visible-light irradiation, arenes undergo oxidant-free hydroxylation, alkoxylation, and amination with high chemoselectivity. In addition to batch reactions, an electrophotocatalytic recirculating flow process is demonstrated, enabling the conversion of benzene to phenol on a gram scale.
- Huang, He,Lambert, Tristan H.
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supporting information
p. 11163 - 11167
(2021/04/19)
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- Aromatic C?H Hydroxylation Reactions with Hydrogen Peroxide Catalyzed by Bulky Manganese Complexes
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The oxidation of aromatic substrates to phenols with H2O2 as a benign oxidant remains an ongoing challenge in synthetic chemistry. Herein, we successfully achieved to catalyze aromatic C?H bond oxidations using a series of biologically inspired manganese catalysts in fluorinated alcohol solvents. While introduction of bulky substituents into the ligand structure of the catalyst favors aromatic C?H oxidations in alkylbenzenes, oxidation occurs at the benzylic position with ligands bearing electron-rich substituents. Therefore, the nature of the ligand is key in controlling the chemoselectivity of these Mn-catalyzed C?H oxidations. We show that introduction of bulky groups into the ligand prevents catalyst inhibition through phenolate-binding, consequently providing higher catalytic turnover numbers for phenol formation. Furthermore, employing halogenated carboxylic acids in the presence of bulky catalysts provides enhanced catalytic activities, which can be attributed to their low pKa values that reduces catalyst inhibition by phenolate protonation as well as to their electron-withdrawing character that makes the manganese oxo species a more electrophilic oxidant. Moreover, to the best of our knowledge, the new system can accomplish the oxidation of alkylbenzenes with the highest yields so far reported for homogeneous arene hydroxylation catalysts. Overall our data provide a proof-of-concept of how Mn(II)/H2O2/RCO2H oxidation systems are easily tunable by means of the solvent, carboxylic acid additive, and steric demand of the ligand. The chemo- and site-selectivity patterns of the current system, a negligible KIE, the observation of an NIH-shift, and the effectiveness of using tBuOOH as oxidant overall suggest that hydroxylation of aromatic C?H bonds proceeds through a metal-based mechanism, with no significant involvement of hydroxyl radicals, and via an arene oxide intermediate. (Figure presented.).
- Masferrer-Rius, Eduard,Borrell, Margarida,Lutz, Martin,Costas, Miquel,Klein Gebbink, Robertus J. M.
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p. 3783 - 3795
(2021/03/09)
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- Highly recyclable Ti0.97Ni0.03O1.97catalyst coated on cordierite monolith for efficient transformation of arylboronic acids to phenols and reduction of 4-nitrophenol
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A stable Ni2+substituted TiO2catalyst (Ti0.97Ni0.03O1.97) has been synthesized by a solution combustion method with an average crystallite size of 7.5 nm. Ti1?xNixO2?x(x= 0.01-0.06) crystallizes in the TiO2anatase structure with Ni2+substituted in Ti4+ion sites and Ni taking a nearly square planar geometry. This catalyst is found to be highly active in the transformation of diverse arylboronic acids to the corresponding phenols. The catalyst coated cordierite monolith can even be recycled for up to 20 cycles with a cumulative TOF of 1.8 × 105h?1. In scale-up reactions, various phenols are synthesized by employing a single cordierite monolith. It also shows high performance in the reduction of 4-nitrophenol.
- Hegde, M. S.,Prasanna,Usha, K. M.
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supporting information
p. 14223 - 14234
(2021/10/25)
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- Catalyst-free rapid conversion of arylboronic acids to phenols under green condition
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A catalyst-free and solvent-free method for the oxidative hydroxylation of aryl boronic acids to corresponding phenols with hydrogen peroxide as the oxidizing agent was developed. The reactions could be performed under green condition at room temperature within very short reaction time. 99% yield of phenol could be achieved in only 1 min. A series of different arenes substituted aryl boronic acids were further carried out in the hydroxylation reaction with excellent yield. It was worth nothing that the reaction could completed within 1 min in all cases in the presence of ethanol as co-solvent.
- Dong, Zhenhua,Liu, Mengmeng,Pan, Hongguo
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- Coordination Polymers as a Functional Material for the Selective Molecular Recognition of Nitroaromatics and ipso-Hydroxylation of Arylboronic Acids
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We report the synthesis and structural characterization of two coordination polymers (CPs), namely; [{Zn(L)(DMF)4} ? 2BF4]α (1) and [{Cd(L)2(Cl)2} ? 2H2O]α (2) (where L=N2,N6-di(pyridin-4-yl)naphthalene-2,6-dicarboxamide). Crystal packing of 1 reveals the existence of channels running along the b- and c-axis filled by the ligated DMF and lattice anions, respectively. Whereas, crystal packing of 2 reveals that the metallacycles of each 1D chain are intercalating into the groove of adjacent metallacycles resulting in the stacking of 1D loop-chains to form a sheet-like architecture. In addition, both 1 and 2 were exploited as multifunctional materials for the detection of nitroaromatic compounds (NACs) as well as a catalyst in the ipso-hydroxylation of aryl/heteroarylboronic acids. Remarkably, 1 and 2 showed high fluorescence stability in an aqueous medium and displayed a maximum 88% and 97% quenching efficiency for 4-NPH, respectively among all the investigated NACs. The mechanistic investigation of NACs recognition suggested that the fluorescence quenching occurred via electron as well as energy transfer process. Furthermore, the ipso-hydroxylation of aryl/heteroarylboronic acids in presence of 1 and 2 gave up to 99% desired product yield within 15 min in our established protocol. In both cases, 1 and 2 are recyclable upto five cycles without any significant loss in their efficiency.
- Bhasin, K. K.,Husain, Ahmad,Kumar, Girijesh,Rani, Pooja
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- Isotruxene-based porous polymers as efficient and recyclable photocatalysts for visible-light induced metal-free oxidative organic transformations
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Two new isotruxene-based porous polymers were prepared and demonstrated to be highly efficient, metal-free heterogeneous photocatalysts for oxidative transformations using air as the mild oxidant under visible-light irradiation. Both catalysts show excellent recyclability. In addition, the reactions can be performed in water, further indicating the greenness of this method. This journal is
- Zhang, Haowen,Zhang, Xiao,Zheng, Ying,Zhou, Cen
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supporting information
p. 8878 - 8885
(2021/11/27)
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- A Dual-Function Highly Crystalline Covalent Organic Framework for HCl Sensing and Visible-Light Heterogeneous Photocatalysis
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Covalent organic frameworks (COFs) offer great potential for various advanced applications such as photocatalysis, sensing, and so on because of their fully conjugated, porous, and chemically stable unique structural architecture. In this work, we have designed and developed a truxene-based ultrastable COF (Tx-COF-2) by Schiff-base condensation between 1,3,5-tris(4-aminophenyl)benzene (TAPB) and 5,5,10,10,15,15-hexamethyl-10,15-dihydro-5H-diindeno(1,2-a:1′,2′-c)fluorene-2,7,12-tricarbaldehyde (Tx-CHO) for the first time. The resulting COF possesses excellent crystallinity, permanent porosity, and high Brunauer-Emmett-Teller (BET) surface areas (up to 1137 m2 g-1). The COF was found to be a heterogeneous, recyclable photocatalyst for efficient conversion of arylboronic acids to phenols under visible-light irradiation, an environmentally friendly alternative approach to conventional metal-based photocatalysis. Besides, Tx-COF-2 provides an immediate naked-eye color change (1 s) and fluorescence "turn-on"phenomena upon exposure to HCl. The response is highly sensitive, with an ultralow detection limit of up to 4.5 nmol L-1.
- Addicoat, Matthew A.,Nailwal, Yogendra,Pal, Santanu Kumar,Wonanke, A. D. Dinga
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p. 6595 - 6604
(2021/07/20)
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- Building a Pyrazole–Benzothiadiazole–Pyrazole Photosensitizer into Metal–Organic Frameworks for Photocatalytic Aerobic Oxidation
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Charge separation plays a crucial role in regulating photochemical properties and therefore warrants consideration in designing photocatalysts. Metal–organic frameworks (MOFs) are emerging as promising candidates for heterogeneous photocatalysis due to their structural designability and tunability of photon absorption. Herein, we report the design of a pyrazole–benzothiadiazole–pyrazole organic molecule bearing a donor–acceptor–donor conjugated π-system for fast charge separation. Further attempts to integrate such a photosensitizer into MOFs afford a more effective heterogeneous photocatalyst (JNU-204). Under visible-light irradiation, three aerobic oxidation reactions involving different oxygenation pathways were achieved on JNU-204. Recycling experiments were conducted to demonstrate the stability and reusability of JNU-204 as a robust heterogeneous photocatalyst. Furthermore, we illustrate its applications in the facile synthesis of pyrrolo[2,1-a]isoquinoline-containing heterocycles, core skeletons of a family of marine natural products. JNU-204 is an exemplary MOF platform with good photon absorption, suitable band gap, fast charge separation, and extraordinary chemical stability for proceeding with aerobic oxidation reactions under visible-light irradiation.
- Jin, Ji-Kang,Wu, Kun,Liu, Xin-Yi,Huang, Guo-Quan,Huang, Yong-Liang,Luo, Dong,Xie, Mo,Zhao, Yifang,Lu, Weigang,Zhou, Xiao-Ping,He, Jian,Li, Dan
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supporting information
p. 21340 - 21349
(2021/12/17)
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- The graphite-catalyzed: ipso -functionalization of arylboronic acids in an aqueous medium: metal-free access to phenols, anilines, nitroarenes, and haloarenes
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An efficient, metal-free, and sustainable strategy has been described for the ipso-functionalization of phenylboronic acids using air as an oxidant in an aqueous medium. A range of carbon materials has been tested as carbocatalysts. To our surprise, graphite was found to be the best catalyst in terms of the turnover frequency. A broad range of valuable substituted aromatic compounds, i.e., phenols, anilines, nitroarenes, and haloarenes, has been prepared via the functionalization of the C-B bond into C-N, C-O, and many other C-X bonds. The vital role of the aromatic π-conjugation system of graphite in this protocol has been established and was observed via numerous analytic techniques. The heterogeneous nature of graphite facilitates the high recyclability of the carbocatalyst. This effective and easy system provides a multipurpose approach for the production of valuable substituted aromatic compounds without using any metals, ligands, bases, or harsh oxidants.
- Badgoti, Ranveer Singh,Dandia, Anshu,Parewa, Vijay,Rathore, Kuldeep S.,Saini, Pratibha,Sharma, Ruchi
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p. 18040 - 18049
(2021/05/29)
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- Cu2O/TiO2 as a sustainable and recyclable photocatalyst for gram-scale synthesis of phenols in water
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A green and straightforward protocol was developed for the synthesis of phenols from aryl boronic acid using an inexpensive and available Cu2O/TiO2 photocatalyst under visible light and sunlight. This approach proceeded in mild reaction conditions in water and the presence of air as a green oxidant, resulting in the corresponding phenols in good to excellent yields. Sunlight was also a sustainable source for this photochemical reaction. Heterogeneous nano photocatalyst was successfully recovered in 8 consecutive runs. It is noteworthy that, the photocatalyst exhibited high activity for the large-scale synthesis of phenols.
- Hosseini-Sarvari, Mona,Keshavarz, Kimia,Tavakolian, Mina
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- Double Insurance of Continuous Band Structure and N-C Layer Induced Prolonging of Carrier Lifetime to Enhance the Long-Wavelength Visible-Light Catalytic Activity of N-Doped In2O3
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Nonmetallic doped metal oxides can be broad in their visible-light-response range. However, the half-filled or isolated impurity state can also be the new recombination center for photogenerated electrons/holes, which seriously influence the photocatalytic activity of the catalyst in the visible-light region. Therefore, how to prolong the photogenerated carrier life of nonmetallic doping metal oxides is the difficult and challenging topic in the field of photocatalysis. In this work, the hexagonal nanosheets assembled by N-doped C (N-C)-coated N-doped In2O3 (N-In2O3) nanoparticles (N-C/N-In2O3 HS) was obtained by simply pyrolyzing the In(2,5-PDC) hexagonal sheets. The N-C/N-In2O3 HS catalyst exhibit good photocatalytic activity and cycle stability in the long-wavelength region of visible light (λ = 520 and 595 nm). The effective utilization of long-wavelength visible light for N-C/N-In2O3 HS was mainly attributed to the acceptor-donor-acceptor compensation mechanism between the oxygen vacancy (VO) and substitutional N-doping (Ns) sites, which made the N-C/N-In2O3 HS possess a continuous band structure, without the half-filled or isolated impurity state in the band gap, and extended its light absorption edge to 733 nm. The compensation mechanism of nitrogen doping on In2O3 can promote the photocatalytic activity under longer-wavelength yellow light (595 nm) irradiation. The N-C layer coated on the N-In2O3 nanoparticles acted as a good acceptor of photogenerated electrons, facilitating the effective spatial separation of photogenerated carriers and extend photogenerated carrier lifetimes. The comparative photocatalytic experiments (N-In2O3 HS and N-C/N-In2O3 HS) show that the presence of N-doped C layer can enhance the photocatalytic efficiency by nearly 10-fold. This double-doping and carbon-coating strategy provided a novel research idea to solve the problem that nonmetal atoms doped metal oxides led to the secondary combination of photogenerated electrons/holes.
- Sun, Liming,He, Xiaoxiao,Zeng, Suyuan,Yuan, Yusheng,Li, Rong,Zhan, Wenwen,Chen, Jinquan,Wang, Xiaojun,Han, Xiguang
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supporting information
p. 1160 - 1171
(2021/01/18)
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- Application of Electron-Rich Covalent Organic Frameworks COF-JLU25 for Photocatalytic Aerobic Oxidative Hydroxylation of Arylboronic Acids to Phenols
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Visible-light-driven organic reactions are environmentally friendly green chemical transformations among which photosynthetic oxidative hydroxylation of arylboronic acids to phenols has attracted increasing research interest during the very recent years. Given the efficiency and reusability of heterogeneous catalysts, COF-JLU25, an electron-rich COF-based photocatalyst constructed by integrating electron-donating blocks 1,3,6,8-tetrakis(4-aminophenyl)pyrene (PyTA) and 4-[4-(4-formylmethyl)-2,5-dimethoxyphenyl] benzaldehyde (TpDA), was selected as a photocatalyst for the oxidative hydroxylation of arylboronic acids. In our studies, COF-JLU25 demonstrated excellent photocatalytic activity with high efficiency, robust reusability, and low catalyst loading, showcasing an application potential of previously underexplored COF-based photocatalyst composed solely of electron-rich units.
- Xiao, Guangjun,Li, Wenqian,Chen, Tao,Hu, Wei-Bo,Yang, Hui,Liu, Yahu A.,Wen, Ke
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supporting information
p. 3986 - 3991
(2021/03/29)
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- β-Diketone boron difluoride dye-functionalized conjugated microporous polymers for efficient aerobic oxidative photocatalysis
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Incorporation of organic chromophores into conjugated micro/mesoporous polymers (CMPs) provides a promising avenue for developing recyclable heterogeneous photocatalysts by overcoming tedious separation and low reusability of homogeneous organic dye-based photocatalysts. However, the design principle and the underlying structure-property relationship for fabricating and selecting various organic dye-embedded CMPs for efficient photocatalysis have not been well-constructed so far. In this study, we described the rational fabrication of two new CMPsviathe one-step Sonogashira coupling using β-diketone boron difluoride dye as the key linker and commonly used building blocks (triphenylamine/triphenylbenzene) as the cores. The resulting boron-dye containing CMPs were efficiently employed as the metal-free photocatalysts in two typical aerobic oxidative organic transformations including coupling of benzylamine and oxidation of aryl boronic acids to corresponding aryl phenols, which have never been explored with other boron-dye-embedded CMPs. They exhibited superior photocatalytic performance compared to their boron-free counterparts due to their wide visible-light absorption, narrow optical bandgaps, and extended π-conjugation due to boron-complexation. The present study establishes β-diketone boron difluoride dyes as efficient building blocks for fabricating new CMP-based photocatalysts.
- Dong, Kaixun,Gong, Weitao,Hassan, Mehdi,Liu, Lu,Ning, Guiling
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p. 3905 - 3913
(2021/06/18)
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- An efficient Ti0.95Cu0.05O1.95 catalyst for ipso – hydroxylation of arylboronic acid and reduction of 4-nitrophenol
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A stable, active and selective Ti0.95Cu0.05O1.95 catalyst, crystallized in anatase TiO2 structure with 5% Cu2+ ions substituted for Ti4+ ions with 5% oxide ion vacancy has been synthesized by solution combustion method. The catalyst was coated over a cordierite monolith (Mg2Al4Si5O18) by solution combustion method. By the first principle density functional theory (DFT) calculations, 48 atoms bulk structure has been optimized and density of states (DOS) has been calculated. Ti – O bond distribution in Ti0.95Cu0.05O1.95 has been compared with pure TiO2. Bond distribution analysis has shown longer Cu – O and Ti – O bonds compared to those in CuO and TiO2 creating Cu2+ and oxide ion vacancy as electrophilic and nucleophilic active sites, respectively. This catalyst was found to be very active for ipso – hydroxylation of arylboronic acid and 4-nitrophenol reduction reactions at room temperature. Catalyst coated cordierite monolith was used in the recycling process of the reaction for 20 cycles and cumulative turnover frequency was found to be 184,840 h?1. Ti0.95Cu0.05O1.95 catalyst coated on cordierite monolith enhanced the rate of the reaction compared to powder catalyst and made the handling and recycling of the catalyst very easy. Graphic abstract: [Figure not available: see fulltext.]
- Bhat, Shrikanth K,Dasappa, Jagadeesh Prasad,Hegde, M. S.,Prasanna
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- Nickel-catalyzed deallylation of aryl allyl ethers with hydrosilanes
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An efficient and mild catalytic deallylation method of aryl allyl ethers is developed, with commercially available Ni(COD)2 as catalyst precursor, simple substituted bipyridine as ligand and air-stable hydrosilanes. The process is compatible with a variety of functional groups and the desired phenol products can be obtained with excellent yields and selectivity. Besides, by detection or isolation of key intermediates, mechanism studies confirm that the deallylation undergoes η3-allylnickel intermediate pathway.
- Ding, Guangni,Fan, Sijie,Wang, Jingyang,Wang, Yu,Wu, Xiaoyu,Xie, Xiaomin,Yang, Liqun,Zhang, Zhaoguo
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supporting information
(2021/09/28)
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- Construction of fully substituted carbon centers containing a heteroatom and a CF3groupvia in situgeneratedp-quinone methides
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1,6-Conjugate additions ofin situgenerated δ-CF3-δ-substitutedp-quinone methides have been achieved with a variety of heteronucleophiles under mild conditions, which led to facile and practical construction of fully substituted carbon centers including a heteroatom and a CF3group. In particular, it was revealed that some amines themselves worked for efficient cleavage of the TBS protective group, and addition of a catalytic amount of an appropriate Br?nsted acid was found to sometimes improve the progress of the desired process.
- Terashima, Kyu,Kawasaki-Takasuka, Tomoko,Yamazaki, Takashi
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p. 1305 - 1314
(2021/02/26)
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- Selective Bromination of β-Positions of Porphyrin by Self-Catalytic Behaviour of VOTPP: Facile Synthesis, Electrochemical Redox Properties and Catalytic Application
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Oxidovanadium(IV) complex of β-octabromo-meso-tetraphenylporphyrin, {[VIVO(TPPBr8)], 2} was synthesized by self-catalytic oxidative bromination of meso-tetraphenylporphyrinatooxidovanadium(IV) {[VIVO(TPP), 1} in excellent yield under mild conditions at 25 °C and its structure was confirmed by single crystal X-ray study. UV-Vis and 1H NMR spectra further confirmed that the meso-phenyl rings are not brominated and thus emphasizes on the selectivity as well as synthetic importance of this catalytic method. In the presence of substrates e. g. phenol derivatives, 1 biomimics the vanadium bromoperoxidase (VBPO) enzyme and catalyses the oxidative bromination of substrates in water at 25 °C. Remarkably, 2 also catalyses the oxidative bromination of phenol derivatives under similar reaction conditions with very high turnover frequency (TOF) values (ca. 29 s?1) along with its recyclability. It was found that 2 showed superior catalytic performance as compared to 1 because of its electron deficient nature due to electron withdrawing bromo substituents and robust saddle shaped nonplanar structure (further supported by DFT studies).
- Maurya, Mannar R.,Prakash, Ved,Avecilla, Fernando,Sankar, Muniappan
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supporting information
p. 1685 - 1694
(2021/05/03)
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- Ni-NiO heterojunctions: a versatile nanocatalyst for regioselective halogenation and oxidative esterification of aromatics
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Herein, we report a facile method for the synthesis of Ni-NiO heterojunction nanoparticles, which we utilized for the nuclear halogenation reaction of phenol and substituted phenols usingN-bromosuccinimide (NBS). A remarkablepara-selectivity was achieved for the halogenated products under semi-aqueous conditions. Interestingly, blocking of thepara-position of phenol offeredortho-selective halogenation. In addition, the Ni-NiO nanoparticles catalyzed the oxidative esterification of carbonyl compounds with alcohol, diol or dithiol in the presence of a catalytic amount of NBS. It was observed that the aromatic carbonyls substituted with an electron-donating group favoured nuclear halogenation, whereas an electron-withdrawing group substitution in carbonyl compounds facilitated the oxidation reaction. In addition, the catalyst was magnetically separated and recycled 10 times. The tuned electronic structure at the Ni-NiO heterojunction controlled selectivity and activity as no suchpara-selectivity was observed with commercially available NiO or Ni nanoparticles.
- Bhardwaj, Nivedita,Goel, Bharat,Indra, Arindam,Jain, Shreyans K.,Singh, Ajit Kumar,Tripathi, Nancy
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supporting information
p. 14177 - 14183
(2021/08/16)
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- Halogenated method of aromatic compound
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The invention belongs to the field of organic synthesis, and particularly relates to synthesis of aromatic halogens, in particular to arylamine. The invention discloses a synthesis method of a corresponding ortho-halogenated product from aromatic compounds such as carbazole and phenol. The method comprises the following steps: adding a metal sulfonate salt catalyst, aromatic amine, carbazole, phenol and other hydrogen - heteroatom-containing aromatic compound reaction substrates, a halogenation reagent and a reaction solvent at a specific reaction temperature. After the drying agent is dried, the yield of the reaction product and the nuclear magnetic characterization determining structure are determined by column chromatography. The reaction product yield is determined by gas chromatography. By adopting the method, under the cheap metal salt catalyst, a plurality of ortho-substituted brominated and chloro products can be obtained with moderate to excellent yield.
- -
-
Paragraph 0199-0201; 0233-0238
(2021/11/10)
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- Visible light-induced mono-bromination of arenes with BrCCl3
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A highly efficient and regioselective bromination of electron-rich arenes and heteroarenes using commercially available BrCCl3as a “Br” source has been developed. The reaction was performed in air under mild conditions with photocatalyst Ru(bpy)3Cl2·6H2O, avoiding the usage of strong acids and strong oxidants. Mono-brominated products were obtained with medium to excellent yields (up to 94%). This strategy has shown good compatibility and highpara-selectivity, which will facilitate the complicated synthesis.
- Fan, Jiali,Wei, Qiancheng,Zhu, Ershu,Gao, Jing,Cheng, Xiamin,Lu, Yongna,Loh, Teck-Peng
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supporting information
p. 5977 - 5980
(2021/06/18)
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- Direct synthesis of sulfinic esters via ultrasound accelerated tandem reaction of thiols and alcohols with N-bromosuccinimide
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The direct transformation of various thiols and simple alcohols with N-bromosuccinimide into sulfinic esters has been investigated by using different categories of base/acidic catalysts as well as co-solvents under varied reaction conditions. The reaction was found out to afford the sulfinic esters with high yields in the absence of catalysts, especially within the shorter time under the acceleration of ultrasonic irradiation than under the longer-lasting conventional stirring conditions.
- Nguyen, Lan-Anh Thi,Le, Tri-Nghia,Duong, Cong-Thang,Vo, Chi-Tam,Duus, Fritz,Luu, Thi Xuan Thi
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p. 519 - 528
(2021/05/27)
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- Aryl phenol compound as well as synthesis method and application thereof
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The invention discloses a synthesis method of an aryl phenol compound shown as a formula (3). All systems are carried out in an air or nitrogen atmosphere, and visible light is utilized to excite a photosensitizer for catalyzation. In a reaction solvent, ArNR1R2 as shown in a formula (1) and water as shown in a formula (2) are used as reaction raw materials and react under the auxiliary action of acid to obtain the aryl phenol compound as shown in a formula (3). The ArNR1R2 in the formula (1) can be primary amine and tertiary amine, can also be steroid and amino acid derivatives, and can also be drugs or derivatives of propofol, paracetamol, ibuprofen, oxaprozin, indomethacin and the like. The synthesis method has the advantages of cheap and easily available raw materials, simple reaction operation, mild reaction conditions, high reaction yield and good compatibility of substrate functional groups. The fluid reaction not only can realize amplification of basic chemicals, but also can realize amplification of fine chemicals, such as synthesis of drugs propofol and paracetamol. The invention has wide application prospect and use value.
- -
-
Paragraph 0075-0079
(2021/05/12)
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- Photocatalytic synthesis of phenols mediated by visible light using KI as catalyst
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A transition-metal-free hydroxylation of iodoarenes to afford substituted phenols is described. The reaction is promoted by KI under white LED light irradiation and uses atmospheric oxygen as oxidant. By the use of triethylamine as base and solvent, the corresponding phenols are obtained in moderate to good yields. Mechanistic studies suggest that KI and catalysis synergistically promote the cleavage of C-I bond to form free aryl radicals.
- Huiqin, Wei,Wu, Mei
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supporting information
(2021/11/30)
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- Selective hydroxylation of aryl iodides to produce phenols under mild conditions using a supported copper catalyst
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Owing to the high activity and low-cost, copper-based catalysts are promising candidates for transforming aromatic halides to yield phenols. In this work, we report the selective hydroxylation of aromatic iodides to produce phenols using an atomically dispersed copper catalyst (Cu-ZnO-ZrO2) under mild reaction conditions. The reactions were conducted without the use of additional organic ligands, and the protection of an inert atmosphere environment is not required. The catalyst can be easily prepared, scalable, and is very efficient for a wide range of substrates. The catalytic reactions can be carried out with only 1.24 mol% Cu loading, which shows great potential in mass production.
- Auni, Anika,Ding, Guodong,Hao, Leiduan,Li, Tao,Li, Xiaoyu,Xu, Haiping,Zhang, Qiang
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p. 25348 - 25353
(2021/08/03)
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- A copper nitride catalyst for the efficient hydroxylation of aryl halides under ligand-free conditions
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Copper nitride (Cu3N) was used as a heterogeneous catalyst for the hydroxylation of aryl halides under ligand-free conditions. The cubic Cu3N nanoparticles showed high catalytic activity, comparable to those of conventional Cu catalysts with nitrogen ligands, demonstrating that the nitrogen atoms in Cu3N act as functional ligands that promote hydroxylation.
- Mitsudome, Takato,Mizugaki, Tomoo,Xu, Hang,Yamaguchi, Sho
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supporting information
p. 6593 - 6597
(2021/08/10)
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- Electrochemical-induced hydroxylation of aryl halides in the presence of Et3N in water
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A thorough study of mild and environmentally friendly electrochemical-induced hydroxylation of aryl halides without a catalyst is presented. The best protocol consists of hydroxylation of different aryl iodides and aryl bromides by water solution in the presence of Et3N under air, affording the target phenols in good isolated yields. Moreover, aryl chlorides were successfully employed as substrates. This methodology also provides a direct pathway for the formation of deoxyphomalone, which displayed a significant anti-proliferation effect.
- Ke, Fang,Lin, Chen,Lin, Mei,Long, Hua,Wu, Mei,Yang, Li,Zhuang, Qinglong
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supporting information
p. 6417 - 6421
(2021/08/03)
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- Biocatalytic Cross-Coupling of Aryl Halides with a Genetically Engineered Photosensitizer Artificial Dehalogenase
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Devising artificial photoenzymes for abiological bond-forming reactions is of high synthetic value but also a tremendous challenge. Disclosed herein is the first photobiocatalytic cross-coupling of aryl halides enabled by a designer artificial dehalogenase, which features a genetically encoded benzophenone chromophore and site-specifically modified synthetic NiII(bpy) cofactor with tunable proximity to streamline the dual catalysis. Transient absorption studies suggest the likelihood of energy transfer activation in the elementary organometallic event. This design strategy is viable to significantly expand the catalytic repertoire of artificial photoenzymes for useful organic transformations.
- Fu, Yu,Huang, Jian,Wu, Yuzhou,Liu, Xiaohong,Zhong, Fangrui,Wang, Jiangyun
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supporting information
p. 617 - 622
(2021/02/03)
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- Decarboxylative Hydroxylation of Benzoic Acids
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Herein, we report the first decarboxylative hydroxylation to synthesize phenols from benzoic acids at 35 °C via photoinduced ligand-to-metal charge transfer (LMCT)-enabled radical decarboxylative carbometalation. The aromatic decarboxylative hydroxylation is synthetically promising due to its mild conditions, broad substrate scope, and late-stage applications.
- Ritter, Tobias,Su, Wanqi,Xu, Peng
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supporting information
p. 24012 - 24017
(2021/10/06)
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- Method for synthesizing heteroatom- substituted aromatic compound from styrene compound
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The invention discloses a method for synthesizing a heteroatom-substituted aromatic compound from a styrene compound, which comprises the following steps of: mixing a styrene compound with a general formula (I) and a heteroatom-containing compound with a general formula (II), and reacting in the presence of an acid additive and an organic solvent to obtain a heteroatom-substituted compound with ageneral formula (III). According to the synthesis method disclosed by the invention, a large amount of styrene compounds are used as raw materials and react to generate aromatic amine or phenol compounds under the action of no metal catalysis; and compared with the traditional aromatic amine and phenol synthesis method, the method has the advantages of high yield, simple conditions, low waste discharge amount, no metal participation, simple reaction equipment, easiness in industrial production and the like.
- -
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Paragraph 0322-0325
(2021/02/06)
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- Alternative method for the synthesis of triazenes from aryl diazonium salts
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An alternative mild method for access to 1-aryl-3,3-dimethyl alkyl triazenes is described. This protocol employs the dropwise addition of a methanolic solution of a carboxylate (RCO2M) or carbonate (CO32?) to a gently heated DMF solution containing an aryl diazonium salt (ArN2+), that had been previously isolated. Presumably homolysis of the weak N–O bond of diazo ether adducts formed in this operation initiates radical pathways that lead to the generation of triazene product. DMF serves as not only a one-electron donor to the diazonium salts employed in this process, but also as a source of dimethylamine radicals that act as a nucleophilic coupling partner. The reaction provides modest yields (ca. 20–40%) across an array of aryl diazonium salts that contain various substitution. Furthermore this unique approach to triazenes contrasts with traditional methods that employ dimethyl amine in reagent form which directly couples with diazonium salts. Seemingly, only one other example employing somewhat similar reaction conditions to this current investigation en route to triazenes has been reported, albeit with lower yields and for one representative example furnished as a side-product. The current work here improves upon the efficiency of this reported result, and further expands the reaction scope.
- Abrams
-
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- Poly-N-bromosulfonamide-melamine as a novel brominating reagent for regioselective ipso-bromination of arylboronic acids
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A practical synthetic method for the synthesis of aryl bromide was developed through regioselective bromination of boronic acid in the presence of poly-N-bromosulfonamide-melamine (PBBSM). In this regard, a novel heterogeneous support, cross-linked poly sulfonamide-melamine, has been successfully synthesized to stabilize bromine with high surface functional group density (6.6?mmol Br+/g). The prepared reagent is a novel brominating reagent that combines the effective functions of N-bromosulfonamide, N-bromosulfonamide-melamine, and melamine groups. The structure of PBBSM was characterized using XRD, FT–IR, 1H NMR, TGA, FE-SEM, EDX, and TGA analysis. Graphic abstract: [Figure not available: see fulltext.]
- Alavinia, Sedigheh,Ghorbani-Vaghei, Ramin
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p. 1269 - 1276
(2021/08/27)
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- Method for hydrolyzing diarylether compound to generate aryl phenol compound
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The invention discloses a method for hydrolyzing a diarylether compound to generate an arylphenol compound. According to the method, visible light is utilized to excite a photosensitizer for catalysis. In a reaction solvent, the raw material in the formula (1) breaks a C (sp2)-O bond under the auxiliary action of acid, and hydrolysis is performed to obtain the bimolecular aryl phenol compounds in the formula (3) and the formula (4). The method can catalyze the reaction at room temperature, is green and environment-friendly, and is easy to operate; the universality is wide, the reaction yield is relatively high, and the tolerance of functional groups is strong; the synthesis method not only can realize small-scale hydrolysis conversion of various diarylether compounds, but also can realize hydrolysis of herbicidal ether, triclosan and a lignin template substrate, and even can realize large-scale hydrolysis of triclosan and the lignin template substrate to realize gram-level degradation. A new strategy is provided for recovering phenol derivatives through lignin hydrolysis, degrading pesticides and purifying wastewater containing a degerming agent or herbicide. The method has wide application prospect and use value.
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Paragraph 0058-0061
(2021/09/29)
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- Method for hydroxylating aromatic compound
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The invention provides a method for directly hydroxylating an aromatic compound. The method comprises the following steps: dissolving the aromatic compound in a solvent, adding hydrogen peroxide and anitroxide free radical compound, and reacting. The nitroxide free radical compound is used as a catalyst, hydrogen peroxide is used as an oxidizing agent, and hydroxylation of the aromatic compound is directly catalyzed and oxidized. Compared with a traditional process, the method has the advantages of high product selectivity, mild reaction conditions, reusability of the catalyst, easiness in separation of oxidation products and raw materials and the like.
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Paragraph 0104-0105
(2020/06/17)
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- Nickel-catalyzed oxidative hydroxylation of arylboronic acid: Ni(HBTC)BPY MOF as an efficient and ligand-free catalyst to access phenolic motifs
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A straightforward and mild oxidative ipso-hydroxylation of arylboronic acids has been achieved using a simple and non-noble metal, nickel-based reusable heterogeneous catalyst Ni(HBTC)BPY MOF (HBTC = benzene-1,3,5-tricarboxylate, BPY = 4,4′-bipyridine) in the presence of benign hydrogen peroxide as an oxidant under ambient reaction condition. The Ni(HBTC)BPY MOF exhibits excellent catalytic activity towards the formation of phenols from diverse arylboronic acids within short time and can be reused up to five times without any notable loss in its activity as well as shown high functional group tolerance even in the presence of sensitive functionalities and useful to achieve hydroxyl group in heterocycles.
- Latha, Ganesapandian,Devarajan, Nainamalai,Karthik, Murugan,Suresh, Palaniswamy
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- Aerobic photooxidative hydroxylation of boronic acids catalyzed by anthraquinone-containing polymeric photosensitizer
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We report herein the synthesis of a polymeric photosensitizer and its application in aerobic photooxidative hydroxylation of boronic acids. The polymeric photosensitizer was synthesized by the condensation of anthraquinone-2-carbonyl chloride (AQ-2-COCl) with poly (2-hydroxyethyl methacrylate) (PHEMA). The photo-oxidative hydroxylation of boronic acids using anthraquinone-containing-poly (2-hydroxyethyl methacrylate) (AQ-PHEMA) was then explored and shown to exhibit high efficiency and broad scope. Moreover, AQ-PHEMA could be easily recovered and reused for more than 20 times without significant loss of the catalytic activity.
- Chen, Yang,Ding, Aishun,Hu, Jianhua
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p. 7927 - 7932
(2020/03/11)
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- Synthesis of Phenols via Metal-Free Hydroxylation of Aryl Boronic Acids with Aqueous TBHP
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An alternate procedure for oxidative hydroxylation of aryl boronic acids with aqueous TBHP to access phenols is described. The protocol tolerated various functional groups substituted with aromatic rings. The reaction was performed in water and free from transition metal oxidants.
- Shaikh, Tanveer MahmadAlli
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- Copper nanoparticles supported on highly nitrogen-rich covalent organic polymers as heterogeneous catalysts for the ipso -hydroxylation of phenyl boronic acid to phenol
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This work describes a simple procedure for the synthesis of highly nitrogen-rich covalent organic polymers using commercially available starting materials like melamine and cyanuric chloride as a solid heterogeneous catalyst Cu/TCOP under solvothermal conditions. The structural properties of the as-synthesized solid heterogeneous catalyst were determined by X-ray diffraction (XRD), diffuse reflectance spectroscopy, Fourier transform infrared (FT-IR) spectroscopy, field emission scanning electron microscopy (FESEM), energy dispersive X-ray spectroscopy (EDS), 13C-CP MAS nuclear magnetic resonance spectroscopy and X-ray photoelectron spectroscopy. The catalytic activity of Cu/TCOP was investigated by focusing on the oxidation of phenylboronic acid under atmospheric conditions in an aqueous medium, achieving a very good yield up to 99%. The reaction performance was evaluated considering the effect of various parameters, such as the amount of the catalyst, reaction time, temperature, and the amount of the base and solvent. The Cu/TCOP catalyst is completely recoverable in a facile manner from the reaction mixture and the efficiency of the copper nanocatalyst can be recovered after five cycles.
- Sadhasivam, Velu,Harikrishnan, Muniyasamy,Elamathi, Ganesan,Balasaravanan, Rajendran,Murugesan, Sepperumal,Siva, Ayyanar
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supporting information
p. 6222 - 6231
(2020/05/13)
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- A scalable and green one-minute synthesis of substituted phenols
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A mild, green and highly efficient protocol was developed for the synthesis of substituted phenols via ipso-hydroxylation of arylboronic acids in ethanol. The method utilizes the combination of aqueous hydrogen peroxide as the oxidant and H2O2/HBr as the reagent under unprecedentedly simple and convenient conditions. A wide range of arylboronic acids were smoothly transformed into substituted phenols in very good to excellent yields without chromatographic purification. The reaction is scalable up to at least 5 grams at room temperature with one-minute reaction time and can be combined in a one-pot sequence with bromination and Pd-catalyzed cross-coupling to generate more diverse, highly substituted phenols.
- Elumalai, Vijayaragavan,Hansen, J?rn H.
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p. 40582 - 40587
(2020/11/18)
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- Bimetallic photoredox catalysis: Visible light-promoted aerobic hydroxylation of arylboronic acids with a dirhodium(ii) catalyst
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We report the use of a rhodium(II) dimer in visible light photoredox catalysis for the aerobic oxidation of arylboronic acids to phenols under mild conditions. Spectroscopic and computational studies indicate that the catalyst Rh2(bpy)2(OAc)4 (1) undergoes metal-metal to ligand charge transfer upon visible light irradiation, which is responsible for catalytic activity. Further reactivity studies demonstrate that 1 is a general photoredox catalyst for diverse oxidation reactions.
- Campbell, Michael G.,Chuang, Gary Jing,Liu, Ming-Lun,Miura-Stempel, Emily,Tu, Jing-Wen,Yang, Hsiang-Ming
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p. 2040 - 2047
(2020/03/13)
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- Iridium complex-linked porous organic polymers for recyclable, broad-scope photocatalysis of organic transformations
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Two rigid porous organic polymers (Ir-POP-1 and Ir-POP-2) were prepared from the coupling reactions of tetraphenylmethane tetraborate and two [Ir(ppy)2(dtbbpy)]+-based bitopic linkers and applied as heterogeneous visible-light photocatalysts for organic transformations. Ir-POP-2 was found to exhibit high catalytic activity for a wide range of organic reactions, which include Smiles-Truce rearrangement of alkyliodides, desulfurative conjugate addition to Michael acceptors, and aerobic oxidations of sulfides and arylboronic acids. For all the transformations, Ir-POP-2 could achieve heterogeneous photocatalytic efficiency that rivals that of the homogeneous prototype iridium complexes. This remarkably high photocatalytic performance has been attributed to the large pore size of the conjugated backbone. The new heterogeneous photocatalyst was also highly stable to achieve good recyclability for all the studied reactions and could be reused eight to nineteen times.
- Xu, Zi-Yue,Luo, Yi,Zhang, Dan-Wei,Wang, Hui,Sun, Xing-Wen,Li, Zhan-Ting
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supporting information
p. 136 - 143
(2020/01/21)
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- Selective oxidative hydroxylation of arylboronic acids by colloidal nanogold catalyzed in situ generation of H2O2 from alcohols under aerobic conditions
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Selective hydroxylation of arylboronic acids was achieved through PVP (polyvinylpyrrolidone)-stabilized nanogold catalyzed in situ generated H2O2 formed by the oxidation of an alcoholic solvent under aerobic conditions. The synthetic application of in situ generated H2O2 was investigated through aerobic epoxidation of (E)-chalcone.
- Sakurai, Hidehiro,Vinsen, Yuta Uetake
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p. 299 - 301
(2020/04/27)
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- Optimizing the crystallization process of conjugated polymer photocatalysts to promote electron transfer and molecular oxygen activation
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Photocatalytic reactive oxygen species (ROS)-induced reactions provide an appealing method to solve the environmental and energy issues, whereas the current oxidation reaction generally suffered from low efficiency and poor selectivity due to uncontrollable O2 activation process. In view of the existence of competitive electron and energy transfer pathway, we propose that highly efficient superoxide radical anion (·O2?) generation can be achieved by optimizing the order degree of the photocatalyst. Herein, by taking carbon nitride polymer as an example, we optimized the crystallization process of carbon nitride polymer by selecting precursors of different polymerization degrees with a molten salt method. Benefiting from the high crystallinity, extended π-conjugated system and strong van der-Waals interactions between interlayers, the modified carbon nitride polymer exhibited accelerated charge transport and enhancement in electron induced molecular oxygen activation reactions under visible light. Consequently, the CCN-P exhibits about 1.5 times higher conversion rate in hydroxylation of phenylboronic acid and over 6-fold faster degradation rate in Rh B organic pollutants photodegradation with respect to pristine carbon nitride. This study provides an in-depth understanding on the optimization of the O2 activation process and the design of advanced photocatalysts.
- Anpo, Masakazu,Cheng, Jiajia,Huang, Caijin,Ou, Honghui,Ren, Wei,Wang, Xinchen
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p. 636 - 645
(2020/07/27)
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- Preparation method of monobrominated aromatic hydrocarbon compound
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The invention discloses a preparation method of a monobrominated aromatic hydrocarbon compound, which comprises the following steps: by using an aromatic hydrocarbon compound as a raw material, wateras a solvent and liquid bromine as a bromine source, reacting at room temperature for 4.5 hours, and after the reaction is finished, carrying out aftertreatment on the obtained reaction mixed solutionto obtain the monobrominated target product. According to the method, a high-selectivity bromination method is realized on the aromatic hydrocarbon compound under the action of water, and the monobrominated aromatic hydrocarbon compound is prepared. The method is high in reaction applicability, mild in condition, high in yield, green and environment-friendly.
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Paragraph 0071-0074
(2020/11/23)
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