- Effect of phosphorus-modification of titania supports on the iridium-catalyzed synthesis of benzimidazoles
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Modification of titania supports for iridium catalysts by phosphorus species greatly enhanced the activity for the synthesis of benzimidazoles via hydrogen transfer. Two series of phosphorus-modified titanias were used: The iridium catalysts supported on phosphorus-doped rutile titania prepared by the hydrothermal method showed nearly 5 times higher activity for the reaction of 2-nitroaniline (1a) and benzyl alcohol (2a) to 2-phenylbenzimidazole (3aa) than the catalysts supported on unmodified rutile. XPS depth profile study substantiated that the dopant was present mainly on the surface of the rutile support. Therefore, a facile wet impregnation method was applied to modify the surface of anatase titania with phosphoric acid. The use of thus-modified titania enhanced the activity of the iridium catalysts by more than 2.7 times. The FTIR and XPS studies revealed the presence of bidentate phosphorus species on the surface of titania, and the H2-TPR study indicated that phosphorus-modification promoted the formation of iridium species reduced at higher temperature, which would be suitable for the present catalysis.
- Yu, Han,Wada, Kenji,Fukutake, Tatsuhiro,Feng, Qi,Uemura, Shinobu,Isoda, Kyosuke,Hirai, Tomomi,Iwamoto, Shinji
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Read Online
- A novel photoaddition of 2-phenylbenzimidazole
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Irradiation of 2-phenylbenzimidazole (3) in the presence of methyl acrylate (20 equivalents) using a medium pressure mercury lamp gives methyl 2-(2-phenylbenzimidazol-1-yl)propionate (4) (75%) whose structure has been confirmed by an X-ray analysis. A similar reaction using acrylonitrile gave only a low yield (1%) of the corresponding propionitrile derivative 5. A mechanism involving photoexcitation of 2-phenylbenzimidazole (3) followed by sequential single electron transfer, proton transfer and radical coupling is proposed to account for the formation of the novel photoadducts 4 and 5.
- Jones, Richard H.,Ramsden, Christopher A.,Rose, Helen L.
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Read Online
- DNA binding, crystal structure, molecular docking studies and anticancer activity evaluation of a copper(II) complex
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A copper complex [Cu(HPBM)(l-Phe)(H2O)]·ClO4(1) (HPBM?=?5-methyl-2-(2′-pyridyl)benzimidazole, l-Phe?=?l-phenylalanine anion) was synthesized and characterized by elemental analysis, IR, ESI–MS, HR–ESI–MS, ESR spectroscopy, and by X-ray single-crystal analysis. The binding constant of the complex with calf thymus DNA (CT-DNA) was determined as 7.38 (±?0.57)?×?104?M?1. Further studies indicated that the complex interacts with CT-DNA through minor groove binding. The in vitro cytotoxic activities of both the free proligand and the complex against Eca-109, HeLa and A549 cancer cells and normal LO2 cells were evaluated by the MTT method. The IC50 values range from 5.7?±?0.1 to 8.3?±?0.6?μM. Free HPBM displays no cytotoxic activity against the selected cancer cells, with IC50 values more than 100?μM. Double staining analysis showed that the complex can induce apoptosis in Eca-109 cells. Comet assays demonstrated that the complex can damage DNA and cause apoptosis. The complex also induces an increase in intracellular reactive oxygen species and a reduction in mitochondrial membrane potential. The complex can also increase the intracellular Ca2+ level and induce release of cytochrome c. The cell cycle arrest was investigated by flow cytometry. The results demonstrate that the complex induces apoptosis in Eca-109 cells through DNA-binding and ROS-mediated mitochondrial dysfunctional pathways.
- Liu, Ya-Xian,Mo, Hui-Wen,Lv, Zhen-Yu,Shen, Fang,Zhang, Chun-Lian,Qi, Yong-Yu,Mao, Zong-Wan,Le, Xue-Yi
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- [Diaquo{bis(p-hydroxybenzoato-κ1O1)}(1-methylimidazole- κ1N1)}copper(II)]: Synthesis, crystal structure, catalytic activity and DFT study
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Metal-organic hybrid complexes often exhibit large surface area, pore volume, fascinating structures and potential applications including catalytic applications. Hence a new metal-organic hybrid complex [Diaquo{bis(p-hydroxybenzoato-κ1O1)}(1-methylimidazole- κ1N1)}copper(II)] was synthesized using conventional method. Physico-chemical characterization of the complex was performed with FTIR spectroscopy, single crystal X-ray diffraction, TGA, EPR and FESEM. Single crystal X-ray diffraction study suggests it to be three dimensional with space group P212121 (orthorhombic). The crystal achieves its three-dimensional structure and stability through extensive intermolecular hydrogen bonding. Hirshfeld surface analysis, catalytic activity and DFT study of the complex was also performed. The synthesized complex acts as good catalyst in benzimidazole synthesis with good recyclability as catalyst up to 5th run.
- Brahman, Dhiraj,Chhetri, Sailesh,Kamath, Amarjit,McArdle, Patrick,Sinha, Biswajit
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- 1-Methylimidazolium ionic liquid supported on Ni@zeolite-Y: fabrication and performance as a novel multi-functional nanocatalyst for one-pot synthesis of 2-aminothiazoles and 2-aryl benzimidazoles
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In the present study, 1-methyl-3-(3-trimethoxysilylpropyl)-1H-imidazol-3-ium chloride-supported Ni@zeolite-Y-based nanoporous materials (Ni@zeolite-Im-IL) were synthesized and their structures were confirmed using different characterization techniques such as FT-IR, FE-SEM, EDX, XRD, BET and TGA-DTG analyses. In order to synthesize this multi-functional nano-system, zeolite-NaY was modified first, with exchanged Ni2+ ions and 3-chloropropyltriethoxysilane (CPTES) as a coupling reagent and then functionalized to imidazolium chloride ionic liquid by N-methylimidazole. New multi-functional nano-material of Ni@zeolite-Im-IL demonstrated high activity in the catalytic synthesis of 2-aminothiazoles 3a–l by one-pot reaction of methylcarbonyls, thiourea and iodine at 80?°C in DMSO with good to excellent yields (85–98%). Also, the catalytic synthesis of 2-aryl benzimidazoles, 6a–m was performed by the condensational reaction of o-arylendiamine and aromatic aldehydes in EtOH at room temperature with excellent yields (90–98%). Advantages of this efficient synthetic strategy include higher purity and shorter reaction time, excellent yield, easy isolation of products, the good stability, activity and feasible reusability of the metallic ionic liquid nanocatalyst. These benefits have made this method more compatible with the principles of green chemistry. Graphical abstract: [Figure not available: see fulltext.]
- Kalhor, Mehdi,Zarnegar, Zohre
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p. 519 - 540
(2021/12/03)
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- Design, preparation, biological investigations and application of a benzoguanamine-based nickel complex for the synthesis of benzimidazoles
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The new magnetic-supported benzoguanamine-based nickel complex was prepared, characterized by various procedures and used as a capable heterogeneous nano-catalyst for the synthesis of diverse 2-phenyl-1H-benzo[d]imidazoles from the reaction o-phenylenedia
- Habibi, Davood,Heydari, Somayyeh,Karamian, Roya,Oliaei, Sajjad,Ranjbar, Nika
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- One-Pot Transformation of Lignin and Lignin Model Compounds into Benzimidazoles
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It is a challenging task to simultaneously achieve selective depolymerization and valorization of lignin due to their complex structure and relatively stable bonds. We herein report an efficient depolymerization strategy that employs 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) as oxidant/catalyst to selectively convert different oxidized lignin models to a wide variety of 2-phenylbenzimidazole-based compounds in up to 94 % yields, by reacting with o-phenylenediamines with varied substituents. This method could take full advantage of both Cβ and/or Cγ atom in lignin structure to furnish the desirable products instead of forming byproducts, thus exhibiting high atom economy. Furthermore, this strategy can effectively transform both the oxidized hardwood (birch) and softwood (pine) lignin into the corresponding degradation products in up to 45 wt% and 30 wt%, respectively. Through a “one-pot” process, we have successfully realized the oxidation/depolymerization/valorization of natural birch lignin at the same time and produced the benzimidazole derivatives in up to 67 wt% total yields.
- Guo, Tao,He, Jianghua,Liu, Tianwei,Zhang, Yuetao
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supporting information
(2022/02/07)
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- Coordination-driven reversible supramolecular assembly formation at biological pH: Trace-level detection of Hg2+ and I? ions in real life samples
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Pyridine coupled bisbenzimidazole probe has been developed for colorimetric sensing of heavy metal pollutants in the aqueous medium. Mechanistic investigation indicates that Hg2+ ions (detection limit: 7.5 ppb) bind to the pyridyl nitrogen ends
- Dey, Nilanjan
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- An Unexpected Formation of 2-Arylbenzimidazoles from α,α-Diiodo-α’-acetoxyketones and o-Phenylenediamines
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An unusual reactivity of the α,α-diiodo-α’-acetoxyketones with o-phenylenediamines is reported through the formation of 2-arylbenzimidazoles. A systematic study through a series of fruitful control experiments and isolation of key intermediates unravelled the unprecedented domino mechanism. This process involves a stepwise two-carbon fragmentation pathway through domino and sequential amidation–aziridination–decarbonylation–I2-mediated aminative cyclization–oxidation reactions. This strategy employs no additives like oxidant, metal catalyst, bases, and represents yet another novel reactivity profile of the building blocks α,α-diiodo-α’-acetoxyketones.
- Sadhukhan, Santu,Mondal, Swagata,Baire, Beeraiah
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- H2 Activation with Co Nanoparticles Encapsulated in N-Doped Carbon Nanotubes for Green Synthesis of Benzimidazoles
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Co nanoparticles (NPs) encapsulated in N-doped carbon nanotubes (Co@NC900) are systematically investigated as a potential alternative to precious Pt-group catalysts for hydrogenative heterocyclization reactions. Co@NC900 can efficiently catalyze hydrogenative coupling of 2-nitroaniline to benzaldehyde for synthesis of 2-phenyl-1H-benzo[d]imidazole with >99 % yield at ambient temperature in one step. The robust Co@NC900 catalyst can be easily recovered by an external magnetic field after the reaction and readily recycled for at least six times without any evident decrease in activity. Kinetic experiments indicate that Co@NC900-promoted hydrogenation is the rate-determining step with a total apparent activation energy of 41±1 kJ mol?1. Theoretical investigations further reveal that Co@NC900 can activate both H2 and the nitro group of 2-nitroaniline. The observed energy barrier for H2 dissociation is only 2.70 eV in the rate-determining step, owing to the presence of confined Co NPs in Co@NC900. Potential industrial application of the earth-abundant and non-noble transition metal catalysts is also explored for green and efficient synthesis of heterocyclic compounds.
- Lin, Chuncheng,Wan, Weihao,Wei, Xueting,Chen, Jinzhu
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p. 709 - 720
(2020/11/30)
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- Preparation method of 2-substituted benzimidazole compound
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The invention discloses a preparation method of a 2-substituted benzimidazole compound, and belongs to the field of synthesis of benzimidazole compounds. The 2-substituted benzimidazole compound is synthesized in an organic solvent by taking an o-nitroaniline compound, aromatic aldehyde, o-dinitrobenzene and aromatic aldehyde as raw materials and taking Co particles wrapped by a nitrogen-doped carbon material as a catalyst. According to the method, the 2-substituted benzimidazole compound can be prepared at room temperature, the reaction conditions are mild, the yield is as high as 95%, the selectivity is as high as 99%, and the method is economical, environmentally friendly and wide in substrate applicability. The used catalyst is easy to prepare, low in cost and good in reusability, canbe separated by utilizing magnetism, and is convenient to recover, so that the method has a relatively strong industrial application prospect.
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Paragraph 0035-0078
(2021/02/20)
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- Transition-Metal-Free Transfer Hydrogenative Cascade Reaction of Nitroarenes with Amines/Alcohols: Redox-Economical Access to Benzimidazoles
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This report describes an efficient transition-metal-free process toward the transfer hydrogenative cascade reaction between nitroarenes and amines or alcohols. The developed redox-economical approach was realized using a combination of KOtBu and Et3SiH as reagents, which allows the synthesis of benzimidazole derivatives via σ-bond metathesis. The reaction conditions hold well over a wide range of substrates embedded with diverse functional groups to deliver the desired products in good to excellent yields. The mechanistic proposal has been depicted on the basis of a series of control experiments, mass spectroscopic evidence which is well supported by density functional theory (DFT) calculations with a feasible energy profile.
- Gujjarappa, Raghuram,Kabi, Arup K.,Malakar, Chandi C.,Musib, Dulal,Roy, Anupam,Sahoo, Abhishek,Singh, Virender,Vodnala, Nagaraju
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p. 14597 - 14607
(2021/11/12)
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- Palladium catalysed hydrolysis-free arylation of aliphatic nitriles for the synthesis of 4-arylquinolin-2-one/pyrazolone derivatives
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Palladium catalysed addition of arylboronic acid to the readily available 2-cyano-(N-aryl)-acetamide or ethyl-2-cyanoacetate followed by subsequent reaction transform them into the biologically significant 4-arylquinolin-2-one or pyrazolone derivatives. The reaction conditions are robust enough to prevent the hydrolysis of ester/amide moiety during arylation. In addition, the unactivated nitrile moiety in the acetonitrile also converted to the corresponding acetophenone derivative.
- Krishna Reddy, Singarajanahalli Mundarinti,Prasanna Kumari, Subramaniyan,Selva Ganesan, Subramaniapillai
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- s-Tetrazine-functionalized hyper-crosslinked polymers for efficient photocatalytic synthesis of benzimidazoles
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Developing green-safe, efficient and recyclable catalysts is crucial for the chemical industry. So far, organic photocatalysis has been proved to be an environmentally friendly and energy-efficient synthetic technology compared with traditional metal catalysis. As a versatile catalytic platform, hyper-crosslinked polymers (HCPs) with large surface area and high stability are easily prepared. In this report, we successfully constructed two porous HCP photocatalysts (TZ-HCPs) featurings-tetrazine units and surface areas larger than 700 m2g?1through Friedel-Crafts alkylation reactions. The rational energy-band structures and coexisting micro- and mesopores endow TZ-HCPs with excellent activities to realize the green synthesis of benzimidazoles (28 examples, up to 99% yield, 0.5-4.0 h) in ethanol. Furthermore, at least 21 iterative catalytic runs mediated by TZ-HCP1D were performed efficiently, with 96-99% yield. This study of TZ-HCPs sheds light on the wide-ranging prospects of application of HCPs as metal-free and green photocatalysts for the preparation of fine chemicals.
- An, Wan-Kai,Zheng, Shi-Jia,Zhang, Hui-Xing,Shang, Tian-Tian,Wang, He-Rui,Xu, Xiao-Jing,Jin, Qiu,Qin, Yuchen,Ren, Yunlai,Jiang, Song,Xu, Cui-Lian,Hou, Mao-Song,Pan, Zhenliang
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supporting information
p. 1292 - 1299
(2021/02/26)
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- Visible-light-mediated organoboron-catalysed metal-free dehydrogenation of N-heterocycles using molecular oxygen
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The surge of photocatalytic transformation not only provides unprecedented synthetic methods, but also triggers the enthusiasm for more sustainable photocatalysts. On the other hand, oxygen is an ideal oxidant in terms of atom economy and environmental friendliness. However, the poor reactivity of oxygen at the ground state makes its utilization challenging. Herein, a visible-light-induced oxidative dehydrogenative process is disclosed, which uses an organoboron compound as the photocatalyst and molecular oxygen as the sole oxidant.Viathis approach, an array of N-heterocycles have been accessed under metal-free mild conditions, in good to excellent yields.
- Wei, Lanfeng,Wei, Yu,Xu, Liang,Zhang, Jinli
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supporting information
p. 4446 - 4450
(2021/06/30)
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- Method for preparing N - heterocyclic ring through visible light mediated dehydrogenation
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The invention discloses a method for preparing N - heterocyclic rings through visible light mediated dehydrogenation, and the reaction can be carried out under the conditions of room temperature and visible light without heating. The novel tetra-coordination N-N - diaryl chelating borate compound serves as a photocatalyst, so that the use of a noble metal photocatalyst is avoided, precious metal residue in the reaction product can be reduced as much as possible, and the method is more suitable for synthesizing bioactive molecules.
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Paragraph 0148-0153
(2021/10/02)
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- Application of sulfonic acid fabricated cobalt ferrite nanoparticles as effective magnetic nanocatalyst for green and facile synthesis of benzimidazoles
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This work represents the design and synthesis of efficient sulfonated cobalt ferrite solid acid catalyst. The synthesized solid acid green catalyst was characterized using various techniques viz. FT-IR, powder XRD, SEM, TEM and VSM. The obtained catalyst was used to synthesize biologically significant 2-substituted benzimidazole derivatives by condensation between o-phenylenediamine with various aromatic, aliphatic and heterocyclic aldehydes. High yield (up to 98 %), short reaction time (10?25 min), mild reaction condition, wide functional group tolerance, easy work-up procedure and excellent values of green chemistry metrices such as lower E factor (0.126), high RME value (88.83 %), carbon efficiency (100 %) and high atom economy (AE) value (90.65 %), are some salient features of the present catalytic system. Moreover, the catalyst recovery by simply using an external magnet and catalyst reusability up to 7 times without any significant loss in catalytic efficiency are some additional remarkable features of the current protocol.
- Yadav, Priyanka,Kakati, Praachi,Singh, Preeti,Awasthi, Satish K.
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- Tetrathienoanthracene-functionalized conjugated microporous polymers as an efficient, metal-free visible-light solid organocatalyst for heterogeneous photocatalysis
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Owing to their advantages of superior inherent porosity, high chemical stability, light weight, and molecularly tunable optoelectronic properties, conjugated microporous polymers (CMPs) have been receiving increasing attention and research interest as pro
- Chang, Jian-Guo,Han, Yin-Feng,Jiao, Guo-Zheng,Li, Qun,Li, Yan-Wei,Nie, Kun,Wang, Chang-An,Zhang, Jian-Ping
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p. 3799 - 3809
(2021/06/18)
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- Cobalt ferrite magnetic nanoparticles as highly efficient catalyst for the mechanochemical synthesis of 2-aryl benzimidazoles
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A highly efficient magnetically separable nano cobalt ferrite catalyst was synthesized via the sol-gel auto combustion method, characterized by powder XRD, SEM, TEM, UV–Visible, FT-IR, magnetic study, and BET isotherm analysis. The synthesized material was found to be an efficient heterogeneous Lewis acid catalyst for the synthesis of 2-aryl benzimidazole derivatives via solvent-free mechanochemical synthesis. The notable features of this new protocol include solvent-free reaction, cost-effectiveness, good yields, and environmental friendliness to afford the products within a short reaction time along with easy recovery and reuse of the nano catalyst.
- Borade, Ravikumar M.,Jadhav, K. M.,Kale, Swati B.,Pawar, Rajendra P.,Tekale, Sunil U.
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- Reusable nano-zirconia-catalyzed synthesis of benzimidazoles and their antibacterial and antifungal activities
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In this article, a zirconia-based nano-catalyst (Nano-ZrO2 ), with intermolecular C-N bond formation for the synthesis of various benzimidazole-fused heterocycles in a concise method is reported. The robustness of this reaction is demonstrated
- Ahmad, Naushad,Ahmed, Faheem,Albalawi, Fadwa,Alomar, Suliman Yousef,Basaveswara Rao, M. V.,Cheedarala, Ravi Kumar,Naidu, Tentu Manohra,Rao, Nalla Krishna,Rao, Tentu Nageswara,Reddy, G. Rajasekhar
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- Two-Step Access to β-Substituted o-Hydroxyphenyl Ethyl Ketones from 4-Chromanone and its Application in Preparation of a Silica-Supported Cobalt(II) Salen Complex
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The o-hydroxyphenyl ethyl ketone skeleton is prevalent in many biologically active natural products and active pharmaceutical ingredients. Herein, a two-step protocol has been developed for synthesis of various β-substituted o-hydroxyphenyl ethyl ketones.
- Guo, Luxia,Ye, Meng,Vaccaro, Luigi,Li, Minghao,Gu, Yanlong
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p. 4754 - 4760
(2021/08/23)
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- Nickel catalyzed sustainable synthesis of benzazoles and purines: Via acceptorless dehydrogenative coupling and borrowing hydrogen approach
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Herein we report nickel-catalyzed sustainable synthesis of a few chosen five-membered fused nitrogen heterocycles such as benzimidazole, purine, benzothiazole, and benzoxazole via acceptorless dehydrogenative functionalization of alcohols. Using a bench stable, easy to prepare, and inexpensive Ni(ii)-catalyst, [Ni(MeTAA)] (1a), featuring a tetraaza macrocyclic ligand (tetramethyltetraaza[14]annulene (MeTAA)), a wide variety of polysubstituted benzimidazole, purine, benzothiazole, and benzoxazole derivatives were prepared via dehydrogenative coupling of alcohols with 1,2-diaminobenzene, 4,5-diaminopyrimidine, 2-aminothiphenol, and 2-aminophenol, respectively. A wide array of benzimidazoles were also prepared via a borrowing hydrogen approach involving alcohols as hydrogen donors and 2-nitroanilines as hydrogen acceptors. A few control experiments were performed to understand the reaction mechanism.
- Chakraborty, Gargi,Guin, Amit Kumar,Mondal, Rakesh,Paul, Nanda
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p. 7217 - 7233
(2021/08/30)
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- Zinc Stabilized Azo-anion Radical in Dehydrogenative Synthesis of N-Heterocycles. An Exclusively Ligand Centered Redox Controlled Approach
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Herein we report an exclusively ligand-centered redox controlled approach for the dehydrogenation of a variety of N-heterocycles using a Zn(II)-stabilized azo-anion radical complex as the catalyst. A simple, easy-to-prepare, and bench-stable Zn(II)-complex (1b) featuring the tridentate arylazo pincer, 2-((4-chlorophenyl)diazenyl)-1,10-phenanthroline, in the presence of zinc-dust, undergoes reduction to form the azo-anion radical species [1b]- which efficiently dehydrogenates various saturated N-heterocycles such as 1,2,3,4-tetrahydro-2-methylquinoline, 1,2,3,4-tetrahydro-isoquinoline, indoline, 2-phenyl-2,3-dihydro-1H-benzoimidazole, 2,3-dihydro-2-phenylquinazolin-4(1H)-one, and 1,2,3,4-tetrahydro-2-phenylquinazolines, among others, under air. The catalyst has further been found to be compatible with the cascade synthesis of these N-heterocycles via dehydrogenative coupling of alcohols with other suitable coupling partners under air. Mechanistic investigation reveals that the dehydrogenation reactions proceed via a one-electron hydrogen atom transfer (HAT) pathway where the zinc-stabilized azo-anion radical ligand abstracts the hydrogen atom from the organic substrate(s), and the whole catalytic cycle proceeds via the exclusive involvement of the ligand-centered redox events where the zinc acts only as the template.
- Das, Siuli,Mondal, Rakesh,Chakraborty, Gargi,Guin, Amit Kumar,Das, Abhishek,Paul, Nanda D.
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p. 7498 - 7512
(2021/06/30)
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- Heterocyclic reaction inducted by Br?nsted–Lewis dual acidic Hf-MOF under microwave irradiation
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Use of green chemistry and alternative strategies has been explored to prepare diverse organic derivatives. The combination between heterogeneous catalyst, environmentally benign reaction and high-yielding methods is gaining momentum. Herein, a defective 6-connected Hf-MOF, named Hf-BTC, was efficiently synthesized and characterized for the heterogeneous catalysis under microwave irradiation. The MOF features including structural defect, porosity, acidity, and stability was analyzed by powder X-ray diffraction, N2 sorption isotherms, acid-base titration, and thermal gravimetric analysis. In the catalytic studies, the Br?nsted-Lewis dual acidic Hf-BTC was efficiently applied for the synthesis of the heterocyclic compounds via the microwave-assisted cycloaddition and condensation reactions. The reactions proceeded smoothly in the presence of the Hf-MOF with a broad scope of substrates provided the expected products in high to excellent yields (up to 99 %) for few minutes and the catalyst could be easily recycle over many consecutive reactions without loss of its reactivity and structure.
- Nguyen, Linh Ho Thuy,Nguyen, Trang Thi Thu,Dang, Minh-Huy Dinh,Tran, Phuong Hoang,Doan, Tan Le Hoang
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- Method for catalytically synthesizing phenylbenzimidazole compound by using copper complex
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The invention relates to a method for catalytically synthesizing a phenylbenzimidazole compound by using a copper complex, which comprises the following steps: in the presence of alkali, taking benzimidazole and halogenated hydrocarbon as raw materials, taking the copper complex containing meta-carborane ligand as a catalyst, and conducting reacting at room temperature to prepare the phenylbenzimidazole compound. Compared with the prior art, the method has the advantages that the halogenated hydrocarbon compound which is low in cost and easy to obtain is used as the substrate, the reaction of benzimidazole and halogenated hydrocarbon is efficiently catalyzed by using the copper complex, the phenylbenzimidazole compound is synthesized by a one-pot method, the reaction condition is mild, the universality is good, the catalytic efficiency is high, few byproducts are produced, the cost is relatively low, the product is easy to separate, and lots of waste residues cannot be generated.
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Paragraph 0031-0034
(2021/08/06)
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- Delivering 2-Aryl Benzoxazoles through Metal-Free and Redox-Neutral De-CF3Process
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An unexpected cleavage of the Csp3-CF3 bond of CF3-hydrobenzoxazoles has been disclosed, affording a range of 2-aryl benzoxazoles under metal-free and redox-neutral conditions. This transformation has demonstrated broad substrate scope and good compatibility of functional groups. 2-Aryl benzothiazole and 2-aryl benzoimidazole could be smoothly assembled in the same manner. On the basis of preliminary mechanistic studies, base initiated and aromatization driven β-carbon elimination was considered to be the key step for the formation of 2. This reaction offers an alternative, facile, and sustainable route to access important 2-aryl benzoxazole motifs.
- Qiao, Xinxin,Zhao, Yong-De,Rao, Mingru,Bu, Zhan-Wei,Zhang, Guangwu,Xiong, Heng-Ying
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p. 13548 - 13558
(2021/10/01)
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- Nitroarenes as versatile building blocks for the synthesis of unsymmetrical urea derivatives and N-Arylmethyl-2-substituted benzimidazoles
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In this contribution, a fast and simple method for the synthesis of unsymmetrical urea derivatives and N-arylmethyl-2-substituted benzimidazoles was developed starting from nitroarenes. The reaction of nitroarenes and phenyl isocyanate or phenyl isothiocyanate in tin (II) chloride dihydrate/choline chloride eutectic mixture afforded the expected urea and thiourea derivatives, while the reaction of different aldehydes with o-nitroaniline or 4-methoxy-2-nitroaniline shows a markedly high preference for the obtention of N-arylmethyl-2-substituted benzimidazoles over the 2-substituted analogues. This method offers a straightforward alternative to obtain the target compounds in good to excellent yields with short reaction times employing an operationally simple experimental set-up. Graphic abstract: [Figure not available: see fulltext.] A series of unsymmetrical urea and thiourea derivatives together with 1,2-disubstituted benzimidazoles are easily obtained in good yields starting from nitroarenes employing the eutectic mixture tin (II) chloride dihydrate/choline chloride as reductive reaction media.
- Rodríguez-Huerto, Paula A.,Pe?a-Solórzano, Diana,Ochoa-Puentes, Cristian
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p. 6275 - 6283
(2021/07/29)
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- UV-visible light-induced photochemical synthesis of benzimidazoles by coomassie brilliant blue coated on W-ZnO@NH2nanoparticles
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Heterogeneous photocatalysts proffer a promising method to actualize eco-friendly and green organic transformations. Herein, a new photochemical-based methodology is disclosed in the preparation of a wide range of benzimidazoles through condensation of o-phenylenediamine with benzyl alcohols in the air under the illumination of an HP mercury lamp in the absence of any oxidizing species catalyzed by a new photocatalyst W-ZnO@NH2-CBB. In this photocatalyst, coomassie brilliant blue (CBB) is heterogenized onto W-ZnO@NH2 to improve the surface characteristics at the molecular level and enhance the photocatalytic activity of both W-ZnO@NH2 and CBB fragments. This unprecedented heterogeneous nanocatalyst is also identified by means of XRD, FT-IR, EDS, TGA-DTG, and SEM. The impact of some influencing parameters on the synthesis route and effects on the catalytic efficacy of W-ZnO@NH2-CBB are also assessed. The appropriate products are attained for both the electron-withdrawing and electron-donating substituents in the utilized aromatic alcohols. Furthermore, preparation of benzimidazoles is demonstrated to occur mainly via a radical mechanism, which shows that reactive species such as ·O2-, OH and h+ would be involved in the photocatalytic process. Stability and reusability studies also warrant good reproducibility of the nanophotocatalyst for at least five runs. Eventually, a hot filtration test proved that the nanohybrid photocatalyst is stable in the reaction medium. Using an inexpensive catalyst, UV-vis light energy and air, as a low cost and plentiful oxidant, puts this methodology in the green chemistry domain and energy-saving organic synthesis strategies. Finally, the anticancer activity of W-ZnO nanoparticles is investigated on MCF7 breast cancer cells by MTT assay. This experiment reveals that the mentioned nanoparticles have significant cytotoxicity towards the selected cell line.
- Chen, Ruijuan,Jalili, Zahra,Tayebee, Reza
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p. 16359 - 16375
(2021/05/19)
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- Cu-Mn Bimetallic Complex Immobilized on Magnetic NPs as an Efficient Catalyst for Domino One-Pot Preparation of Benzimidazole and Biginelli Reactions from Alcohols
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An efficient magnetically recyclable bimetallic catalyst by anchoring copper and manganese complexes on the Fe3O4 NPs was prepared and named as Fe3O4@Cu-Mn. It was founded as a powerful catalyst for the domino one-pot oxidative benzimidazole and Biginelli reactions from benzyl alcohols as a green protocol in the presence of air, under solvent-free and mild conditions. Fe3O4@Cu-Mn NPs were well characterized by FT-IR, XRD, FE-SEM, TEM, VSM, TGA, EDX, DLS, and ICP analyses. The optimum range of parameters such as time, temperature, amount of catalyst, and solvent were investigated for the domino one-pot benzimidazole and Biginelli reactions to find the optimum reaction conditions. The catalyst was compatible with a variety of benzyl alcohols, which provides favorable products with good to high yields for all of derivatives. Hot filtration and Hg poisoning tests from the nanocatalyst revealed the stability, low metal leaching and heterogeneous nature of the catalyst. To prove the synergistic and cooperative effect of the catalytic system, the various homologues of the catalyst were prepared and then applied to a model reaction separately. Finally, the catalyst could be filtered from the reaction mixture simply, and reused for five consecutive cycles with a minimum loss in catalytic activity and performance. Graphic Abstract: A new magnetically recyclable Cu/Mn bimetallic catalyst has been developed for domino one-pot oxidation-condensation of benzimidazole and Biginelli reactions from alcohols. [Figure not available: see fulltext.]
- Nasseri, Mohammad Ali,Rezazadeh, Zinat,Kazemnejadi, Milad,Allahresani, Ali
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p. 1049 - 1067
(2020/09/11)
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- Selective C-C bonds formation, N-alkylation and benzo[d]imidazoles synthesis by a recyclable zinc composite
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Earth abundant metals are much less expensive, promising, valuable metals and could be served as catalysts for the borrowing hydrogen reaction, dehydrogenation and heterocycles synthesis, instead of noble metals. The uniformly dispersed zinc composites were designed, synthesized and carefully characterized by means of XPS, EDS, TEM and XRD. The resulting zinc composite showed good catalytic activity for the N-alkylation of amines with amines, ketones with alcohols in water under base-free conditions, while unsaturated carbonyl compounds could also be synthesized by tuning the reaction conditions. Importantly, it was the first time to realize the synthesis of 2-aryl-1H-benzo[d]imidazole derivatives by using this zinc composite under green conditions. Meanwhile, this zinc catalyst could be easily recovered and reused for at least five times.
- Duan, Zheng-Chao,Wang, Dawei,Ye, Dongdong,Zhu, Guanxin,Zhu, Haiyan
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supporting information
(2021/08/06)
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- Ionic-Liquid-Catalyzed Synthesis of Imines, Benzimidazoles, Benzothiazoles, Quinoxalines and Quinolines through C?N, C?S, and C?C Bond Formation
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We report the tetramethyl ammonium hydroxide catalyzed oxidative coupling of amines and alcohols for the synthesis of imines under metal-free conditions by utilizing oxygen from air as the terminal oxidant. Under the same conditions, with ortho-phenylene diamines and 2-aminobenzenethiols the corresponding benzimidazoles and benzothiazoles were obtained. Quinoxalines were obtained from ortho-phenylene diamines and 1-phenylethane-1,2-diol, the conditions were then extended to the synthesis of quinoline building blocks by reaction of 2-amino benzyl alcohols either with 1-phenylethan-1-ol or acetophenone derivatives. The formation of C?N, C?S and C?C bonds was achieved under metal-free conditions. A broad range of amines (aromatic, aliphatic, cyclic and heteroaromatic) as well as benzylic alcohols including heteroaryl alcohols reacted smoothly and provided the desired products. The mild reaction conditions, commercially available catalyst, metal-free, good functional-group tolerance, broad range of products (imines, benzimidazoles, benzothiazoles, quinoxalines and quinolines) and applicability at gram scale reactions are the advantages of the present strategy.
- Adimurthy, Subbarayappa,Badhani, Gaurav,Joshi, Abhisek
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p. 6705 - 6716
(2021/12/31)
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- Pyridyl bridged NNP cobalt complex and application thereof
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The invention relates to a pyridyl bridged NNP cobalt complex and an application thereof. A pyridyl bridged tridentate NNP compound is used as a ligand to react with a metal cobalt precursor to obtainthe pyridyl bridged NNP cobalt complex. The complex can be used for catalyzing dehydrogenation condensation of o-phenylenediamine and benzyl alcohol to generate benzimidazole compounds. The method has the advantages of cheap and easily available raw materials, simple operation, few synthesis steps, green reaction and the like.
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Paragraph 0049-0051
(2021/01/12)
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- Hydrogen Auto-transfer Synthesis of Quinoxalines from o-Nitroanilines and Biomass-based Diols Catalyzed by MOF-derived N,P Co-doped Cobalt Catalysts
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A Co-based heterogeneous catalyst supported on N,P co-doped porous carbon (Co@NCP) is prepared via a facile in-situ doping-carbonization method. The Co@NCP composite features a large surface area, high pore volume, high-density and strong basic sites. Furthermore, doping of P atoms can regulate the electronic density of Co. Therefore, Co@NCP exhibits good performance for the synthesis of quinoxalines from o-nitroanilines and biomass-derived diols under alkali-free conditions.
- Sun, Kangkang,Li, Dandan,Lu, Guo-Ping,Cai, Chun
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p. 373 - 381
(2020/12/09)
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- Functional POM-catalyst for selective oxidative dehydrogenative couplings under aerobic conditions
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Development of selective and efficient reusable catalytic systems for sustainable chemical production under benign conditions is attractive and received much attention. Herein, we report a rod-shaped octadecyl trimethylammonium functionalized Keggin-type polyoxometalate [PMO12O40] hybrids (OTA-POM) as an efficient heterogeneous catalyst for selective oxidative dehydrogenative couplings under aerobic conditions without any additive or external base. The catalyst recovery and subsequent five successive recyclability studies of hybrid POM confirms the heterogeneous nature of present catalytic system.
- Samaraj, Elavarasan,Balaraman, Ekambaram,Manickam, Sasidharan
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- Visible light initiated oxidative coupling of alcohols ando-phenylenediamines to synthesize benzimidazoles over MIL-101(Fe) promoted by plasmonic Au
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The use of visible light to initiate one-pot synergistic/cascade reactions is a green and energy saving strategy. In this manuscript, we report that MIL-101(Fe) can act as a multifunctional catalyst to realize the oxidative condensation betweeno-phenylenediamines and alcohols to synthesize benzimidazoles under visible light. The deposition of plasmonic Au nanoparticles (Au NPs) on MIL-101(Fe) led to significantly improved activity. Both controlled experiments and electron spin resonance (ESR) results revealed that the production of benzimidazoles fromo-phenylenediamines and alcohols involves three sequential steps,i.e., the oxidative dehydrogenation of alcohols to produce aldehydes, the condensation betweeno-phenylenediamines and the aldehydes to produce Schiff bases and their oxidation to form benzimidazoles,viaa superoxide radical (O2˙?)-mediated pathway. The promoting effect of plasmonic Au NPs in this reaction can be ascribed to the effective transfer of the surface plasmon resonance (SPR)-excited hot electrons to the lowest unoccupied molecular orbital (LUMO) of MIL-101(Fe), which led to the generation of more active O2˙?radicals. This study not only provides a green and sustainable way for the synthesis of benzimidazoles, but also highlights the great potential of using rationally designed plasmonic metal NP/MOF nanocomposites as multifunctional catalysts for light initiated one-pot tandem/cascade reactions.
- Hao, Mingming,Li, Zhaohui,Qin, Yuhuan,Xu, Chao
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p. 4161 - 4169
(2021/06/17)
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- Photocatalytic green synthesis of benzazoles from alcohol oxidation/toluene sp3C-H activation over metal-free BCN: effect of crystallinity and N-B pair exposure
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Porous borocarbonitride (P-BCN), with the characteristics of enhanced crystallinity and improved N-B pair exposure, was prepared with a simple KCl-assisted molten salt strategy. Efficient heterogeneous photocatalytic tandem synthesis of benzazoles from alcohol oxidation/toluene sp3C-H activation was achieved firstly over the metal-free P-BCN using visible light and the green oxidant O2, with only water as a by-product. Variouso-thio/hydroxy/aminoanilines and alcohols or toluenes could be converted to the corresponding 2-substituted benzothiazoles, benzoxazoles and benzimidazoles with good to excellent photocatalytic performance. The improved photocatalytic performance in comparison to bulk BCN should be due to the crystallinity-enhancement-induced improvement in charge separation and transmission. The increased N-B pair exposure promoted superoxide radical generation due to the electron-enriched N atoms, as well as improved oxidation ability due to the valence band constructed by the B 2p orbital. This work presents a green and efficient synthetic strategy towards benzazoles and other fine chemicalsviametal-free heterogeneous photocatalysis.
- Cheng, Hongmei,Gao, Xue,Jiang, Heyan,Sun, Bin,Zang, Cuicui
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p. 7955 - 7962
(2021/12/27)
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- [Re(η6-C6H5-benzimidazole)2]+ and Derivatives as Dye Mimics; Synthesis, UV Absorption Studies and DFT Calculations
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Functionalizations of highly oxidation and hydrolysis stable mono-cationic rhenium bis-arene complexes [Re(η6-C6H6)2]+ are of great interest. We directly built up structural features of the well-known Hoechst Dye on the coordinated arenes as a model for prospective DNA minor groove binding studies. Extensions of the aromatic bis-arene unit with functionalized and derivatized benzimidazole moieties resulted in a deep orange colour of the complexes, showing UV/Vis absorption spectra with multiple transition maxima. These have been assigned with support of DFT calculations to gain information about their charge transfer natures. The different transitions of the complexes, which are either intra-ligand, ligand-to-ligand or metal-to-ligand charge transitions, were additionally compared and discussed with the spectra of the corresponding free ligands.
- Gotzmann, Carla,Blacque, Olivier,Fox, Thomas,Alberto, Roger
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supporting information
p. 2493 - 2498
(2021/06/01)
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- Host–Guest Interactions in a Metal–Organic Framework Isoreticular Series for Molecular Photocatalytic CO2 Reduction
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A strategy to improve homogeneous molecular catalyst stability, efficiency, and selectivity is the immobilization on supporting surfaces or within host matrices. Herein, we examine the co-immobilization of a CO2 reduction catalyst [ReBr(CO)3(4,4′-dcbpy)] and a photosensitizer [Ru(bpy)2(5,5′-dcbpy)]Cl2 using the isoreticular series of metal–organic frameworks (MOFs) UiO-66, -67, and -68. Specific host pore size choice enables distinct catalyst and photosensitizer spatial location—either at the outer MOF particle surface or inside the MOF cavities—affecting catalyst stability, electronic communication between reaction center and photosensitizer, and consequently the apparent catalytic rates. These results allow for a rational understanding of an optimized supramolecular layout of catalyst, photosensitizer, and host matrix.
- Casini, Angela,Fischer, Roland A.,Haimerl, Johanna,Rieger, Bernhard,Schuster, Michael,Shustova, Natalia B.,Stanley, Philip M.,Thomas, Christopher,Urstoeger, Alexander,Warnan, Julien
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p. 17854 - 17860
(2021/06/11)
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- Visible-Light Photoredox Catalyzed Double C-H Functionalization: Radical Cascade Cyclization of Ethers with Benzimidazole-Based Cyanamides
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A visible-light photoredox catalyzed radical cascade cyclization of simple ethers with cyanamides is developed at room temperature. This strategy involves sequential inert Csp3-H/Csp2-H functionalizations through intermolecular addition reaction of oxyalkyl radicals to N-cyano groups followed by radical cyclization of iminyl radicals in situ generated with C-2 aryl rings. This method allows for efficient synthesis of tetracyclic benzo[4,5]imidazo[1,2-c]quinazolines. Importantly, this is the first example of an intermolecular-intramolecular radical cascade cyclization reaction of cyanamides.
- Jiang, Si,Tian, Xiao-Jing,Feng, Shu-Yao,Li, Jiang-Sheng,Li, Zhi-Wei,Lu, Cui-Hong,Li, Chao-Jun,Liu, Wei-Dong
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supporting information
p. 692 - 696
(2021/02/01)
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- Synthesis, characterization and biological evaluation of benzimidazole and benzindazole derivatives as anti-hypertensive agents
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A substituted benzimidazole and benzindazole derivatives had been synthesized having antihypertensive activity through antagonizing the angiotensin II (Ang II) receptors. The in vivo antihypertensive activity of the compounds was done with acute renal hypertension model. Two compounds TG 1 and TG 3 were found to have antihypertensive activity comparable to Telmisartan which is a prototype for Angiotensin II receptor antagonists class of drugs.In an antihypertensive study the compounds TG 1, TG 2 and TG 3 had systolic blood pressures of 147.2 mm/Hg, 168.2 mm/Hg, and 126.3 mm/Hg, respectively. This systolic blood pressure was lower than the disease control vehicle-treated rodents, which had a systolic blood pressure of 167.2 mm/Hg. The diastolic blood pressure was 119.7 mm/Hg, 124.7 mm/Hg and 88.83 mm/Hg, respectively and that of the disease control vehicle-treated rodents was 122.3 mm/Hg. TG 3 had comparable decrease in the MABP to Telmisartan. These encouraging results make compound TG 3 effective anti-hypertensive drug candidate and worthy of further investigation.
- Silky, Sethy,Mandal, Sudip Kumar,Ewies, Ewies Fawzy,Neerupma, Dhiman,Arun, Garg
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p. 3659 - 3664
(2021/07/10)
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- 1,2-Dibutoxyethane-Promoted Oxidative Cleavage of Olefins into Carboxylic Acids Using O2 under Clean Conditions
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Herein, we report the first example of an effective and green approach for the oxidative cleavage of olefins to carboxylic acids using a 1,2-dibutoxyethane/O2 system under clean conditions. This novel oxidation system also has excellent functional-group tolerance and is applicable for large-scale synthesis. The target products were prepared in good to excellent yields by a one-pot sequential transformation without an external initiator, catalyst, and additive.
- Ou, Jinhua,Tan, Hong,He, Saiyu,Wang, Wei,Hu, Bonian,Yu, Gang,Liu, Kaijian
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p. 14974 - 14982
(2021/10/25)
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- Oxy-sulfonylation of terminal alkynesviaC-S coupling enabled by copper photoredox catalysis
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We report the first literature example using visible light-induced trimethylsilyl azide (TMS-N3)-assisted copper-catalyzed oxy-sulfonylation of terminal C-C bonds to form β-keto sulfones (C-S bond formation). TMS-N3promotes the reaction by facilitating the formation of sulfonyl radicals, which later decompose into N2gas upon light irradiation. This method involves the use of commercially available and stable starting materials. Also, a wide range of functional groups have been well-tolerated under the current photoredox process, evading the side product formation. Potent biologically active compounds, such as CES1, 11β-HSD1 inhibitors, anti-analgesic agents, and reactive synthesis intermediates were synthesized to demonstrate the synthetic utility of the current methodology. Moreover, green chemistry metrics and Eco-scale evaluation for the current photochemical method show that the protocol is eco-friendly and highly efficient.
- Charpe, Vaibhav Pramod,Das, Deb Kumar,Hwang, Kuo Chu,Hwu, Jih Ru,Lin, Chun-Cheng,Pampana, V. K. K.,Sagadevan, Arunachalam
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p. 3569 - 3574
(2021/06/06)
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- A TEMPO-Functionalized Ordered Mesoporous Polymer as a Highly Active and Reusable Organocatalyst
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The properties of high stability, periodic porosity, and tunable nature of ordered mesoporous polymers make these materials ideal catalytic nanoreactors. However, their application in organocatalysis has been rarely explored. We report herein for the first time the incorporation of a versatile organocatalyst, 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO), into the pores of an FDU-type mesoporous polymer via a pore surface engineering strategy. The resulting FDU-15-TEMPO possesses a highly ordered mesoporous organic framework and enhanced stability, and shows excellent catalytic activity in the selective oxidation of alcohols and aerobic oxidative synthesis of 2-substituted benzoxazoles, benzimidazoles and benzothiazoles. Moreover, the catalyst can be easily recovered and reused for up to 7 consecutive cycles.
- Guo, Ying,Wang, Wei David,Li, Shengyu,Zhu, Yin,Wang, Xiaoyu,Liu, Xiao,Zhang, Yuan
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p. 3689 - 3694
(2021/09/29)
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- A heterogeneous catalytic strategy for facile production of benzimidazoles and quinoxalines from primary amines using the Al-MCM-41 catalyst
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This study reports a straightforward heterogeneous catalytic (Al-MCM-41) approach to synthesize nitrogen heterocycle moieties from primary amines under solvent-free conditions. The Al-MCM-41 catalyst was prepared using a hydrothermal method and characterized by various analytical techniques. The probability and limitations of the catalytic methodology were presented with various substrates. The catalytic method grants an attractive route to a wide variety of benzimidazole and quinoxaline moieties with good to excellent yields. The gram scale reaction and reusability (up to five cycles) of the Al-MCM-41 catalyst would greatly benefit industrial applications. This journal is
- Vasu, Amrutham,Naresh, Mameda,Krishna Sai, Gajula,Divya Rohini, Yennamaneni,Murali, Boosa,Ramulamma, Madasu,Ramunaidu, Addipilli,Narender, Nama
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supporting information
p. 9439 - 9446
(2021/12/09)
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- Visible light promoted tandem dehydrogenation-deaminative cyclocondensation under aerobic conditions for the synthesis of 2-aryl benzimidazoles/quinoxalines fromortho-phenylenediamines and arylmethyl/ethyl amines
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Visible light promoted domino synthesis of 2-aryl benzimidazoles is reported through the reaction ofortho-phenylenediamines and arylmethyl amines under aerobic conditions. The methodology has wide substrate scope and tolerates a wide range of functional groups affording the products in high yields. The use of arylethyl amines instead of arylmethyl amines gives 2-aryl quinoxalines.
- Sofi, Firdoos Ahmad,Sharma, Rohit,Rawat, Ravi,Chakraborti, Asit K.,Bharatam, Prasad V.
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supporting information
p. 4569 - 4573
(2021/03/22)
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- K2S2O8activation by glucose at room temperature for the synthesis and functionalization of heterocycles in water
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While persulfate activation at room temperature using glucose has primarily been focused on kinetic studies of the sulfate radical anion, the utilization of this protocol in organic synthesis is rarely demonstrated. We reinvestigated selected K2S2O8-mediated known organic reactions that invariably require higher temperatures and an organic solvent. A diverse, mild functionalization and synthesis of heterocycles using the inexpensive oxidant K2S2O8 in water at room temperature is reported, demonstrating the sustainability and broad scope of the method. Unlike traditional methods used for persulfate activation, the current method uses naturally abundant glucose as a K2S2O8 activator, avoiding the use of higher temperature, UV light, transition metals or bases.
- Hunjan, Mandeep Kaur,Laha, Joydev K.
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p. 8437 - 8440
(2021/09/02)
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- Copper-catalyzed regioselective 2-amination of o-haloanilides with aqueous ammonia
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An efficient Cu(II)-vasicine catalytic system has been developed for intramolecular C[sbnd]N bond formation. In this way, regioselective 2-amination of o-haloanilides with aqueous ammonia in EtOH has been achieved. This strategy provides several advantages, such as good regioselectivity, high yields and functional group tolerance.
- Tang, Yan-Ling,Li, Mei-Ling,Gao, Jin-Chun,Sun, Yun,Qu, Lu,Huang, Feng,Mao, Ze-Wei
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- Molecular Oxygen-Mediated Radical Cyclization of Acrylamides with Boronic Acids
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A radical alkylarylation of 2-aryl-N-methacryloyl indoles via autoxidation of alkylboronic acids was developed under metal-free conditions for the construction of indolo[2,1-a]isoquinolinone derivatives. Primary and secondary alkyl boronic acids were utilized as suitable alkyl sources with O2 as the clean and green oxidant in a simple operate mode. Moreover, this protocol can also be applied to the construction of benzimidazo-[2,1-a]isoquinolinone derivatives. (Figure presented.).
- Pan, Changduo,Yuan, Cheng,Yu, Jin-Tao
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p. 4889 - 4893
(2021/09/09)
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- Possible competitive modes of decarboxylation in the annulation reactions ofortho-substituted anilines and arylglyoxylates
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Annulation reactions ofortho-substituted anilines and arylglyoxylates in the presence of K2S2O8at 80 °C under metal-free neutral conditions have been investigated, which extended a platform for the tandem synthesis of nitrogen heterocycles. While arylglyoxylic acids are known to undergo decarboxylation to form an acyl radical in the presence of K2S2O8and used in the Minisci acylation of electron-deficient (hetero)aromatics, their reactions with electron-richortho-substituted anilines to form nitrogen heterocycles have recently been studied. Depending upon the experimental conditions used in the reactions, the mechanism of the formation of heterocycles involving reactions of an acyl radical or aryl iminocarboxylic acids has been postulated. Given the subtle understanding of the mechanisms of annulation reactions of 2-substituted anilines and arylglyoxylates in the presence of K2S2O8, an extensive mechanistic investigation was undertaken. In the current study, the various mechanistic pathways including the generation of acyl, imidoyl, aminal, and N,O-hemiketal radicals have been postulated based on different possible decarboxylation modes. Some of the proposed intermediates are supported based on the available analytical data. The protocol uses a single, inexpensive reagent K2S2O8, which offers not only transition-metal-free conditions but also serves as the reagent for the key decarboxylation step. Taken together, this study complements the current development of the annulation reactions of 2-substituted anilines and arylglyoxylates in terms of synthesis and mechanistic understanding.
- Laha, Joydev K.,Panday, Surabhi,Tomar, Monika,Patel, Ketul V.
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supporting information
p. 845 - 853
(2021/02/09)
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- Tandem imine formationviaauto-hydrogen transfer from alcohols to nitro compounds catalyzed by a nanomagnetically recyclable copper catalyst under solvent-free conditions
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A direct imination reaction was developed by tandem reaction of alcohols and nitro compounds in the presence of Cu-isatin Schiff base-γ-Fe2O3as a nanomagnetically recyclable catalyst under solvent-free conditions. By this method, various imines were prepared in good to high yields from one-pot reaction of various alcohols (primary aromatic and aliphatic) and nitro compounds (aromatic and aliphatic)viaan auto-hydrogen transfer reaction. Use of an inexpensive and easily reusable catalyst, without requiring any additives or excess amounts of benzyl alcohol as the reaction solvent are the other advantages of this method. This catalytic system has the merits of cost effectiveness, environmental benignity, excellent recyclability and good reproducibility.
- Derakhshan, Seyed Ruhollah,Hosseini Moghadam, Hadis,Sansano, José Miguel,Sobhani, Sara
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p. 19121 - 19127
(2021/06/03)
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- Iron-Catalyzed Hydrogen Transfer Reduction of Nitroarenes with Alcohols: Synthesis of Imines and Aza Heterocycles
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A straightforward and selective reduction of nitroarenes with various alcohols was efficiently developed using an iron catalyst via a hydrogen transfer methodology. This protocol led specifically to imines in 30-91% yields, with a good functional group tolerance. Noticeably, starting from o-nitroaniline derivatives, in the presence of alcohols, benzimidazoles can be obtained in 64-72% yields when the reaction was performed with an additional oxidant, DDQ, and quinoxalines were prepared from 1,2-diols in 28-96% yields. This methodology, unprecedented at iron for imines, also provides a sustainable alternative for the preparation of quinoxalines and benzimidazoles.
- Wu, Jiajun,Darcel, Christophe
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supporting information
p. 1023 - 1036
(2021/01/09)
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- Solvent-dependent metal-free chemoselective synthesis of benzimidazoles and 1,3,5-triarylbenzenes from 2-amino anilines and aryl alkyl ketones catalyzed by I2
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A solvent-dependent I2-catalyzed chemoselective reaction was developed for the synthesis of benzimidazoles and 1,3,5-triarylbenzenes via the annulation of 2-amino anilines and aryl alkyl ketones or the cyclization of aryl alkyl ketones, respectively. With 1,4-dioxane as the solvent, sequential C[sbnd]N bond formation followed by C(CO)-C(CH3) bond cleavage leads to the formation of benzimidazoles in a highly selective manner while aldol-type self-condensation of aryl alkyl ketones predominates using PhNO2 or PhCl as the solvent to afford 1,3,5-triarylbenzenes.
- Ding, Yuxin,Ma, Renchao,Ma, Yongmin
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supporting information
(2021/04/09)
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