- DMF-Assisted Radical Cyclization of o-Isocyanodiaryl Ethers via 1,5-Aryl Migration: Construction of 2-Arylbenzoxazoles
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A novel DMF-assisted radical cyclization of o-isocyanodiaryl ethers via 1,5-aryl migration has been developed for the synthesis of a series of 2-arylbenzoxazoles by the FeCl3/TBHP/Et3N catalytic system in DMF. However, N,N-dimethylbenzo[d]thiazole-2-carboxamide and N,N-dimethylbenzo[d]selenazole-2-carboxamide were obtained from the corresponding substrate 2-isocyanophenyl p-methoxyphenyl thioether and 2-isocyanodiphenyl selenoether under the same conditions. A possible mechanism may involve aryl 1,5-migration and DMF-assisted radical cyclization of o-isocyanodiaryl ethers.
- Cai, Jingyu,Ding, Qiuping,Peng, Yiyuan,Song, Zhibin,Tan, Yuxing,Ye, Xiaoling,Yuan, Sitian
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p. 1485 - 1492
(2022/01/20)
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- An efficient rapid synthesis of benzoxazoles and benzothiazoles using pma.Sio2 at room temperature under heterogeneous conditions
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Treatment of 2-aminophenol (or 2-aminothiophenol) with aromatic aldehydes in the presence of phosphomolybdic acid on silica at room temperature affords the corresponding benzoxazoles (or benzothiazoles) in excellent yields (88-96%) under heterogeneous conditions. Benzoxazoles and benzothiazoles are formed in less than 10 min.
- Sudhakar, Chithaluri,Shekhar, Vanam,Shyamsunder, Manchi,Suryakumari, Adurthi,Manojkumar, Vala
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p. 583 - 587
(2021/09/30)
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- Syntheses, characterization, and catalytic potential of novel vanadium and molybdenum Schiff base complexes for the preparation of benzimidazoles, benzoxazoles, and benzothiazoles under thermal and ultrasonic conditions
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A new ONO-tridentate Schiff base ligand (H2L) derived from 3-methoxysalicylaldehyde and nicotinic hydrazide was synthesized and characterized by elemental analysis, FT-IR, 1H NMR, 13C NMR, UV–Vis, and powder XRD studies. Then, oxovanadium(V) and dioxomolybdenum(VI) Schiff base complexes, VOL and MoO2L, were also prepared and characterized by different techniques. Moreover, the catalytic activities of both complexes were investigated for the synthesis of benzimidazoles, benzoxazoles, and benzothiazoles under reflux conditions as well as through ultrasonic irradiation. The results revealed several advantages of this procedure, including high product yields, short reaction times, facile work-up procedure, simplicity in operation, eco-friendly reaction conditions, and green aspects by avoiding toxic catalysts and solvents. Graphic abstract: [Figure not available: see fulltext.]
- Kargar, Hadi,Kargar, Khadijeh,Fallah-Mehrjardi, Mehdi,Munawar, Khurram Shahzad
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p. 593 - 605
(2021/06/21)
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- Fluorinated phosphoric acid as a versatile effective catalyst for synthesis of series of benzimidazoles, benzoxazoles and benzothiazoles at room temperature
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The present work describes synthesis of a series of benzimidazoles, benzoxazoles and benzothiazoles through the cyclization of 1, 2-phenylenediamine, 2-aminothiophenol, or 2-aminophenol with aryl, aliphatic and heteroaryl aldehydes. The present synthetic protocol is very much efficient in presence of 5 mol % fluorophosphoric acid as a catalyst in ethanol solvent at room temperature. Shorter reaction time, simple work-up technique, high yields and easy availability are specific compensations of the present synthetic approach.
- Mathapati, Sushil R.,Patil, Komal N.,Mathakari, Sujit S.,Suryawanshi, Appasaheb W.,Jadhav, Arvind H.
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p. 538 - 547
(2021/01/21)
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- Dowex 50W: A green mild reusable catalyst for the synthesis of 2-aryl benzoxazole derivatives in aqueous medium
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In this work simple efficient, one pot and environmentally friendly method was developed for the synthesis of 2-Aryl-1H-benzoxazole derivatives at 80oC using ortho-aminophenol and various aldehydes. It has been found that Dowex 50W is an effective catalyst to prepare moderate to high yield of a variety of benzoxazole derivatives through a clean and simple process. Aqueous medium, green methodology, rapid reaction, reusability of heterogeneous catalyst are the great advantages of this protocol.
- Datta, Arup
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p. 341 - 347
(2021/05/19)
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- Heterogeneous palladium (II)-complexed dendronized polymer: A rare palladium catalyst for the one-pot synthesis of 2-arylbenzoxazoles
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The palladium complex of dendronized amine polymer (EG–Gn–Pd, n = 0, 1 and 2) having ethylene glycol-initiated polyepichlorohydrin as core was synthesized on a Merrifield resin support and was well characterized. Generally, palladium catalysts are known for carbon–carbon coupling reactions. Here, a developed catalyst was found to be good for benzoxazole synthesis. Higher generation dendronized polymer (EG–G2–Pd) was found to be better catalyst over lower generation dendronized polymers. Moreover, dendronized polymers were found to be a better catalyst over dendrigraft polymers. The catalyst reusability was checked and good yield was obtained for five cycles.
- George, Smitha,Sreekumar, Krishnapillai
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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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- 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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- Production process of fluorescent whitening agent OB-1
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The invention relates to a production process of a fluorescent whitening agent OB-1. The production process specifically comprises the following steps: 1, carrying out condensation reaction on p-toluic acid and o-aminophenol to generate 4-methyl phenyl benzoxazole; 2, carrying out distillation treatment after the condensation reaction is finished, and collecting a main fraction 4-methyl intermediate; 3, adding methanol into the main fraction, keeping the temperature at 60 DEG C for 6 hours, cooling to 10 DEG C, centrifugally filtering, drying, and transferring into a vulcanization synthesis kettle; 4, carrying out a vulcanization synthesis reaction on the 4-methyl intermediate to generate OB-1, rinsing with xylene, repeatedly washing with xylene, and drying the xylene by distillation to obtain a dried OB-1 crude product; 5, adding trichlorobenzene, the OB-1 crude product and activated carbon into a refining kettle to refine OB-1; and 6, pulping and washing OB-1 with methanol, carryingout centrifugal separation, and drying a filtering cake to obtain the OB-1 product. The method is environmentally friendly, safe and high in yield.
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Paragraph 0030; 0037; 0039-0047
(2021/03/11)
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- Stable Pd(0) Complexes with Ferrocene Bisphosphanes Bearing Phosphatrioxaadamantyl Substituents Efficiently Catalyze Selective C-H Arylation of Benzoxazoles by Aryl Chlorides
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Versatile applications and unique performance of 1,1’-bis(diphenylphosphanyl)ferrocene (dppf) in coordination chemistry and catalysis prompted the search for its analogs. This contribution describes the synthesis of the first donor-unsymmetric dppf congeners bearing bulky and rigid 1,3,5,7-tetramethyl-2,4,6-trioxa-8-phosphaadamantyl (CgP) donor groups, viz. Ph2PfcPCg (1) and Ph2PfcCH2PCg (2; fc=ferrocene-1,1’-diyl). Bis-phosphanes 1 and 2 were converted into air-stable Pd(0) complexes, [Pd(ma)(L^L)] (L^L=1 and 2; ma=maleic anhydride). Together with [Pd(ma)(dppf)], these complexes were applied as catalysts in Pd-catalyzed C?H arylation of benzoxazoles with aryl chlorides in n-butanol as an environmentally benign solvent. Among all catalysts tested in this study, complex [Pd(ma)(2)] performed the best, providing a high-yield and selective synthesis of 2-arylbenzoxazoles from a range of the generally less reactive chloroarenes at low catalyst loading (typically 1 mol.%). Under similar conditions, the structurally related heterocycles (e. g., 1-methylbenzimidazole and benzothiazole) did not react.
- Horky, Filip,Císa?ová, Ivana,?těpni?ka, Petr
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p. 4848 - 4856
(2021/10/12)
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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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- TEMPO-mediated aerobic oxidative synthesis of 2-aryl benzoxazoles via ring-opening of benzoxazoles with benzylamines
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A simple and efficient TEMPO-mediated system for aerobic oxidative synthesis of 2-aryl benzoxazoles from readily available benzoxazoles and primary benzylic and hetero benzylic amines is presented in one pot. The reaction proceeds through the ring-opening of benzoxazoles and is followed by oxidative condensation with benzylamines. These metal-free, straightforward reactions worked well with a wide range of substrates, yielding moderate to good yields under mild conditions using air as an external green oxidant.
- Rao, Mugada Sugunakara,Hussain, Sahid
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p. 2684 - 2694
(2021/07/26)
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- Pd/Cu-Catalyzed C-H/C-H Cross Coupling of (Hetero)Arenes with Azoles through Arylsulfonium Intermediates
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A highly efficient method for the selective formal C-H/C-H cross-coupling of azoles and (hetero)arenes was established through arylsulfonium intermediates under transition-metal catalysis, which produced a variety of 2-(hetero)aryl azoles in good to excellent yields. Advantages of the reaction included mildness, a good functional group tolerance, a wide range of substrates, a high regio- and chemoselectivity, one-pot procedures, and the late-stage functionalization of complex molecules without the use of oxidants, offering a promising strategy for the transition-metal-catalyzed C-H arylation of azoles.
- Lin, Zeng-Hui,Tian, Ze-Yu,Zhang, Cheng-Pan
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supporting information
p. 4400 - 4405
(2021/06/27)
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- Novel and efficient heterogeneous polymer supported copper catalyst for synthesis of 2-substituted Benzoxazoles from 2-Haloanilides
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A novel polymer supported copper complex is prepared by the immobilization of copper iodide on chemically modified polyacrylonitrile and its application in heterogeneous catalysis is described. The catalyst was prepared by easy method via synthetic modification of Polyacrylonitrile (PAN) using ethylene diamine followed by the complexation with CuI. After characterization, this complex was explored as a green and efficient heterogeneous catalyst for the synthesis of 2-benzoxazoles from 2-haloanilides. The reaction was performed without adding additional ligand and the catalyst shows activity over a broad range of substrates with quantitative product yields. The catalyst was easily recovered by simple filtration and reused successfully for further cycle.
- Saranya, Thachora Venu,Sruthi, Pambingal Rajan,Raj, Veena,Anas, Saithalavi
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- Investigation of Pd-PEPPSI catalysts and coupling partners towards direct C2-arylation/heteroarylation of benzoxazole
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2-Aryl/heteroaryl-substituted benzoxazoles are important heterocyclic motifs extensively found in several bioactive molecules, pharmaceuticals and natural products. In view of the importance of these compounds, there is need to develop easiest and simplest synthetic routes. The motive of this current work is to conduct the direct C2-arylation reaction on benzoxazole with various cross-coupling partners like aryl/heteroaryl halide/carboxylic acid/diazonium tetrafluoroborate/sulfonyl chloride/boronic acids in the presence of different symmetrical and unsymmetrical Pd-PEPPSI (pyridine-enhanced pre-catalyst preparation by stabilization initiation) catalysts via C (sp2)–C (sp2) bond formation. Compared with other coupling partners, boronic acids coupled with benzoxazole very efficiently in the presence of sterically and electronically tunable bulky1,3-bis(N,N′-2,4,6-triisopropylbenzyl)benzimidazolium-Pd-PEPPSI complex in open air to offer the corresponding C2-aryl/heteroaryl benzoxazole compounds. Further, it is worthy to mention that there is no need of any external oxidant/ligand/additive for the complete conversion of starting molecules to products. The reactions progressed successfully with a wide range of substrate scope and attained the products in good to excellent yields in a short reaction time in ethanol/water (1:1) medium. Greatly, catalysts can be recovered and reused for few cycles with significant reactivity.
- Gokanapalli, Anusha,Motakatla, Venkata Krishna Reddy,Peddiahgari, Vasu Govardhana Reddy
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- Synthetic method 2 -aryl benzoxazole derivative (by machine translation)
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The invention discloses a synthesis method of 2 -aryl benzoxazole derivative, which comprises the following steps: reacting o-nitrophenol derivative with an aryl formaldehyde derivative in the presence of a pyridine accelerant and an elemental sulfur reducing agent to obtain 2 -arylbenzoxazole derivative. (by machine translation)
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Paragraph 0044-0051; 0058-0061; 0063-0067; 0072-0075
(2020/06/05)
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- Photoinduced Heterogeneous C?H Arylation by a Reusable Hybrid Copper Catalyst
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Heterogeneous copper catalysis enabled photoinduced C?H arylations under exceedingly mild conditions at room temperature. The versatile hybrid copper catalyst provided step-economical access to arylated heteroarenes, terpenes and alkaloid natural products with various aryl halides. The hybrid copper catalyst could be reused without significant loss of catalytic efficacy. Detailed studies in terms of TEM, HRTEM and XPS analysis of the hybrid copper catalyst, among others, supported its outstanding stability and reusability.
- Choi, Isaac,Müller, Valentin,Lole, Gaurav,K?hler, Robert,Karius, Volker,Vi?l, Wolfgang,Jooss, Christian,Ackermann, Lutz
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supporting information
p. 3509 - 3514
(2020/03/03)
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- Visible Light-Induced Copper-Catalyzed C—H Arylation of Benzoxazoles?
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A general method for visible light-induced copper-catalyzed arylation of sp2 C—H bonds of azoles has been developed. The method employs aryl halide as the coupling partner, lithium alkoxide as base. A variety of azoles including benzooxazole and benzothiazole can be arylated. Furthermore, electron-poor heterocycles such as thiophene possessing one electron-withdrawing group can also be arylated.
- Ma, Xiaodong,Zhang, Guozhu
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supporting information
p. 1299 - 1303
(2020/08/05)
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- Phosphine-phosphonium ylides as ligands in palladium-catalysed C2-H arylation of benzoxazoles
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As balanced electron-rich P,C-chelating ligands, phosphine-phosphonium-ylides are considered for their ability to in situ promote palladium-catalysed direct C(sp2)–H arylation. Using methyl phosphonium salts of 2,2'-bis(diphenylphosphino)-1,1'-binaphtyl (“methyl-BINAPIUM”) as ylide precursors under optimized reaction conditions, arylation of benzoxazole was found to proceed in moderate to high yield to give functional 2-aryl benzoxazoles. A strong anion effect of the non-salt free ylide was evidenced (TfO? > I? > PF6? ≈ salt-free). This first example of phosphonium ylides as ligands in catalytic C–H activation extends the prospect of their general implementation in homogeneous transition metal catalysis.
- Yao, Zhenyu,Lin, Xing,Chauvin, Remi,Wang, Lianhui,Gras, Emmanuel,Cui, Xiuling
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p. 3250 - 3254
(2020/05/25)
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- Synthesis and X-ray crystal structures of three new nickel(II) complexes of benzoylhydrazones: Catalytic applications in the synthesis of 2-arylbenzoxazoles
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Three new complexes of nickel(II), having general formula [Ni(L1)(PPh3)] (1), [Ni(L1)(4-picoline)] (2), and [Ni(L2)(4-picoline)] (3) were synthesized by the reaction of Ni(OAc)2·4H2O with corresponding benzolyhydrazine-derived Schiff base ligands i.e. [4-(diethylamino)-2-hydroxybenzylidene]-benzohydrazonic acid (H2L1) or [2-(hydroxynaphthalen-1-yl)methylene]-benzohydrazonic acid (H2L2) and PPh3/4-picoline as co-ligand in 1:1:1 ratio in methanol. All the three complexes were air-stable, isolated as reddish brown solids and characterized by Elemental analysis, FT-IR, 1H, 13C{1H}, 31P{1H} NMR spectroscopy and mass spectrometry. The structures of all three complexes were determined by single crystal X-ray diffraction studies which revealed the distorted square planar geometry of the complexes. In these complexes, three coordination sites were occupied by ONO pincer type Schiff base ligand and the fourth site was blocked by phosphorus (P) or nitrogen (N) atom of the co-ligand. The catalytic potential of all three complexes was explored in the synthesis of a series of 2-arylbenzoxazoles from aldehydes and 2-aminophenol, using low catalyst loading (0.5 mol%). Complex 1 was found to be the best catalyst among three complexes, for the synthesis of a series of 2-aryl benzoxazoles. The ease of synthesis, air-stability and robustness of the catalyst, and good TONs are some of the key characteristics of the described catalytic system.
- Layek, Samaresh,Agrahari, Bhumika,Kumar, Akash,Dege, Necmi,Pathak, Devendra D.
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- Straightforward synthesis of benzoxazoles and benzothiazoles via photocatalytic radical cyclization of 2-substituted anilines with aldehydes
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Eosin Y-catalyzed one-pot coupling and cyclization of o-substituted anilines with aldehydes to form benzoxazoles and benzothiazoles under mild condition has been developed. The reaction scope was broadly tolerant of various 2-substituted anilines and aldehydes. The desired products were obtained in high yields with the use of eosin Y as a photocatalyst under a substantial refinement of reaction conditions in comparison with previous literature. Based on the experimental results observed, a plausible mechanism involving a radical process has been proposed.
- Le, Hao Anh Nguyen,Nguyen, Long Hoang,Nguyen, Quynh Nhu Ba,Nguyen, Hai Truong,Nguyen, Khang Quoc,Tran, Phuong Hoang
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- In-vitro Anti-cancer assay and apoptotic cell pathway of newly synthesized benzoxazole-N-heterocyclic hybrids as potent tyrosine kinase inhibitors
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A series of benzoxazole-N-heterocyclic hybrids have been synthesized by a one-pot strategy. Molecular docking study revealed that such compounds have the ability to inhibit enzyme protein tyrosine kinase. The findings of this work have been the successful synthesis of benzoxazole scaffolds, featuring hybrids of benzoxazole with quinoline and quinoxaline respectively. The molecular docking studies have showed these compounds to be inhibitors of tyrosine kinase enzyme which triggers growth of cancer cells. The cytotoxicity study of compounds 4a-f showed better potency against breast cancer cell lines MCF-7 and MDA-MB-231 in contrast to oral and lung cancer cell lines KB and A549. The tyrosine kinase activity was measured using Universal Tyrosine Kinase Assay kit using horseradish peroxide (HRP)-conjugated anti-phosphotyrosine kinase solution as a substrate. The compounds 4c exhibited maximum inhibition in the activity of enzyme tyrosine kinase with IC50 value 0.10 ± 0.16 μM, than other compounds which were studied and thus proved to be inhibitors of enzyme tyrosine kinase. The selective index of all four compounds was found out to be greater than two, indicating the non-toxic behaviour, i.e. good anti-cancer activity. Further, fluorescence microscopic study helped to characterize the mode of cell death, which was found to be late apoptosis as indicated by the orange fluorescence. The SAR analysis has also been carried out.
- Desai, Sulaksha,Desai, Vidya,Shingade, Sunil
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supporting information
(2019/11/13)
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- Sulfur-Promoted Synthesis of Benzoxazoles from 2-Aminophenols and Aldehydes
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Elemental sulfur (S8) was found to be an excellent stoichiometric oxidant to promote oxidative condensation of 2-aminophenols with a wide range of aldehydes, including aliphatic aldehyde such as cyclohexanecarboxaldehyde. The reactions were catalyzed by sodium sulfide in the presence of DMSO as an additive. The benzoxazole products were obtained in satisfactory yields. The reaction conditions could be applied to larger syntheses (10–50 mmol).
- Nguyen, Le Anh,Dang, Thai Duy,Ngo, Quoc Anh,Nguyen, Thanh Binh
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supporting information
p. 3818 - 3821
(2020/06/10)
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- Sulfur/DABCO Promoted Reductive Coupling/Annulation Cascade Reaction between o -Hydroxy/Amino Nitrobenzenes and Benzaldehydes
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Sulfur/DABCO was found to be an efficient reagent in promoting- the reductive coupling/annulation of o -nitrophenols or o -nitroanilines with benzaldehydes. This method represents a simple, straightforward, and green approach to the construction of benz-oxazoles and benzimidazoles.
- Dang, Minh-Huy Dinh,Nguyen, Linh Ho Thuy,Tran, Phuong Hoang
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supporting information
p. 1687 - 1694
(2020/05/25)
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- Acid-promoted cleavage of the C–C double bond of N-(2-Hydroxylphenyl)enaminones for the synthesis of benzoxazoles
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An acid-mediated selective cleavage of C–C double bond of N-(2-hydroxylphenyl)enaminones with formation a new C–O bond for the synthesis of 2-substituted benzoxazoles has been developed. This protocol proceeds under transition metal- and oxidant-free conditions with broad functional group tolerance. The oxidative cleavage of C–C double bond of N-(2-hydroxylphenyl)enaminone is also realized using NCS or NFSI as oxidants with release of 2,2-dihalogen-acetophenone fragments.
- Ge, Bailu,Peng, Yanling,Liu, Jing,Wen, Si,Peng, Cheng,Cheng, Guolin
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- Pyrazole-3-carboxylates assisted N-heterocyclic carbene palladium complexes: synthesis, characterization, and catalytic activities towards arylation of azoles with arylsulfonyl hydrazides
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Four mononuclear and dinuclear pyrazole-3-carboxylates assisted NHC–Pd complexes have been synthesized and characterized. Notably, the bridge-cleavage reactions of [Pd(μ-Cl)(Cl)(NHC)]2 with 1H-pyrazole-3-carboxylic acid afforded dinuclear complexes [(NHC)Pd(μ-1H-pyrazolato-3-carboxylate)]2, in which the 1H-pyrazolato-3-carboxylate was employed as a N^N^O dianionic chelating and bridging ligand. To further explore the structural features and catalytic properties of the complexes, 1-methyl-1H-pyrazole-3-carboxylic acid was introduced into the coordination with [Pd(μ-Cl)(Cl)(NHC)]2 and the corresponding mononuclear complexes (NHC)PdCl(1-methyl-1H-pyrazole-3-carboxylate) were obtained. The catalytic properties of the complexes in desulfitative arylation of azoles with arylsulfonyl hydrazides were initially investigated.
- Yang, Jin
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- Iron(0)-Catalyzed Transfer Hydrogenative Condensation of Nitroarenes with Alcohols: A Straightforward Approach to Benzoxazoles, Benzothiazoles, and Benzimidazoles
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The iron-catalyzed hydrogen transfer strategy has been applied to the redox condensation of o-hydroxynitrobenzene with alcohol, leading to the formation of benzoxazole derivatives. A wide range of 2-substituted benzoxazoles were synthesized in good to excellent yields without the addition of an external redox agent. A series of control experiments provided a plausible mechanism. Furthermore, the reaction system was successfully extended to the synthesis of benzothiazoles and benzimidazoles.
- Putta, Ramachandra Reddy,Chun, Simin,Choi, Seung Hyun,Lee, Seok Beom,Oh, Dong-Chan,Hong, Suckchang
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p. 15396 - 15405
(2020/12/02)
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- Efficient Cu-catalyzed intramolecular: O -arylation for synthesis of benzoxazoles in water
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An efficient method was developed for synthesis of benzoxazoles by Cu-catalyzed intramolecular O-arylation of o-halobenzanilides in water. This strategy provides several advantages, such as high yields, water as a green solvent and functional groups tolerance.
- Gao, Hui,Li, Minxin,Mao, Zewei,Rao, Gaoxiong,Tang, Yanling
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p. 14317 - 14321
(2020/04/23)
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- Method for synthesizing benzoxazole through microwave radiation of benzamide compound in water phase
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The invention discloses a method for synthesizing benzoxazole through microwave radiation of a benzamide compound in a water phase. The benzamide compound is added into the water phase under the microwave condition to be subjected to a cyclization reaction for generating the benzoxazole under the alkali condition, and the method for preparing the benzoxazole is environmentally friendly, easy and convenient to operate, safe, low in cost and efficient. Compared with the prior art, the method can be applied to a large number of functional groups, the yield is high, the number of by-products is small, and the method is easy to operate, safe, low in cost and environmentally friendly. (Please see the specifications for the formula).
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Paragraph 0024
(2019/03/08)
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- Method used for rapid preparation of benzo-heterocycle compound with physical grinding under solvent-free room temperature conditions
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The invention discloses a method used for rapid preparation of benzo-heterocycle compound with physical grinding under solvent-free room temperature conditions. According to the method, glacial aceticacid is taken as a catalyst; at solvent-free room temperature conditions, physical grinding is adopted, reaction of 2-substituted arylamines (2-mercapto arylamine, 2-aminophenol, and o-phenylenediamine) and aromatic aldehydes is carried out using physical grinding. The method is friendly to the environment, is simple in operation, is safe, is low in cost, and is high in efficiency. Compared withthe prior art, the advantages are that: the method is suitable for a large amount of functional groups, yield is high, less by-product is generated, operation is simple, the method is safe, cost is low, and the method is friendly to the environment.
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Paragraph 0062; 0063
(2019/01/21)
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- Mixed N-heterocycles/N-heterocyclic carbene palladium(II) allyl complexes as precatalysts for direct arylation of azoles with aryl bromides
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A series of mixed N-heterocycles/N-heterocyclic carbene palladium(II) allyl complexes with general formula [(NHC)Pd(η3-allyl)]2(μ2-N-heterocycles)(BF4)2 were prepared in one pot based on anion metathesis of (NHC)Pd(η3-allyl)Cl complexes and then ligand replacement with N-heterocycles [N-heterocycles = pyrazine (pyz), 4,4′-bipyridine (bpy) and trans-4,4′-bipyridylethylene (bpe)]. The solid-state structures shown dinuclear structures with two palladium(II) centers holding together by bridged N-heterocycles. Initially investigation of the obtained complexes as precatalysts for direct C[sbnd]H bond arylation of azoles with aryl bromides was carried out.
- Yang, Jin
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p. 2182 - 2187
(2019/02/24)
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- Hemoglobin: A New Biocatalyst for the Synthesis of 2-substituted Benzoxazoles via Oxidative Cyclization
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Efficient and mild synthesis of a series of 2-substituted benzoxazoles via oxidative cyclization catalyzed by hemoglobins reported here for the first time. Satisfactory yields (84 %–97 %) and mild reaction conditions make this method highly viable for practical applications.
- Li, Fengxi,Li, Zhengqiang,Tang, Xuyong,Cao, Xinyu,Wang, Chunyu,Li, Jialin,Wang, Lei
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p. 1192 - 1195
(2019/02/07)
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- A New Pathway to 2-Arylbenzoxazoles and 2-Arylbenzothiazoles Via One-Pot Oxidative Cyclization Reactions Under Iron-Organic Framework Catalysis
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Iron-organic framework MOF-235 was synthesized, and consequently utilized as a productive heterogeneous catalyst for the synthesis of 2-arylbenzoxazoles and 2-arylbenzothiazoles via one-pot oxidative cyclization reactions between 2-aminophenols or 2-aminothiophenols and alcohols. The transformation was considerably controlled by the oxidant and the nature of solvent, and the system of di-tert-butylperoxide with xylene led to best yield of major products. The MOF-235 catalyst presented higher catalytic efficiency for the synthesis of 2-arylbenzoxazoles and 2-arylbenzothiazoles than a number of MOF-based catalysts and established homogeneous catalysts. Recovering and reutilizing the framework catalyst for the cyclization transformation was possible while its catalytic activity was retained. To the best of our knowledge, this iron-catalyzed one-pot oxidative transformation to produce 2-arylbenzoxazoles and 2-arylbenzothiazoles under heterogeneous catalysis conditions was not previously reported in the literature.
- Doan, Son H.,Tran, Chau B.,Cao, An. L. N.,Le, Nhan T. H.,Phan, Nam T. S.
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p. 2053 - 2063
(2019/04/25)
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- Iodine Promoted One-Pot Synthesis of 2-Aryl Benzoxazoles from Amidoximes via Oxidative Cyclization and Ring Contraction
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A molecular I2-promoted one-pot synthesis of 2-aryl benzoxazoles has been developed by using amidoximes rather than the limited 2-aminophenols or 2-haloamides as substrates. The amidoxime substrates provided unique and efficient strategies for converting readily available aniline and benzaldehyde precursors into valuable chemicals. This transformation proceeded smoothly under transition-metal-free conditions through a sequential oxidative cyclization and ring contraction, and provided a potential route for introducing certain groups at any site of the scaffold.
- Zhang, Yong,Ji, Min
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supporting information
p. 7506 - 7510
(2019/11/28)
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- Transition-Metal-Free Alkylation/Arylation of Benzoxazole via Tf2O-Activated-Amide
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A transition-metal-free approach to the alkylation/arylation of benzoxazole was developed by employing Tf2O-activated-amide as the alkylating/arylating reagent. The mild reaction conditions, and particularly insensitivity to air and water, further enhance the synthetic potential in pharmaceutical synthesis. (Figure presented.).
- Niu, Zhi-Jie,Li, Lian-Hua,Liu, Xue-Yuan,Liang, Yong-Min
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p. 5217 - 5222
(2019/11/13)
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- Palladium-catalyzed direct C2-arylation of azoles with aromatic triazenes
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A highly efficient palladium-catalyzed arylation of azoles at the C2-position using 1-aryltriazenes as aryl reagents was developed. Azoles including oxazoles, thiazoles, imidazoles, 1,3,4-oxadiazoles, and oxazolines could react with 1-aryltriazenes smoothly to generate the corresponding products in good to excellent yields, and various substitution patterns were tolerated toward the reaction.
- Liu, Can,Wang, Zhiming,Wang, Lei,Li, Pinhua,Zhang, Yicheng
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p. 9209 - 9216
(2019/11/05)
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- A 2 - substituted benzoxazole derivative of the preparation method
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The invention discloses a 2 - substituted benzoxazole derivative of the preparation method, its reaction as follows: . The present invention can be 2 - substituted pyrrole derivatives, acetophenone derivatives can be obtained and at the same time 2, 2 - dihalo acetophenone derivatives; and through the C (sp2 ) - C (sp2 ) At the same time selectively fracture of the aromatization. The method of the invention the resulting raw materials are easy, high yield, mild reaction conditions, the reaction time is short, wide substrate range, reaction specificity is strong, easy post treatment and green environmental protection.
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Paragraph 0054-0057
(2019/07/04)
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- Cesium Fluoride and Copper-Catalyzed One-Pot Synthesis of Benzoxazoles via a Site-Selective Amide C?N Bond Cleavage
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We report herein a two-step one-pot strategy for the synthesis of benzoxazoles from amides by using cesium fluoride/copper as catalysts. This approach involves the in situ generation of acyl fluorides from the corresponding amides, and the acyl fluorides undergo transamidation and cyclization to give benzoxazoles in good yields. In this work, the amide C?N bonds are activated by CsF to form the acyl fluoride intermediates, which further react with o-bromoanilines to efficiently yield benzoxazoles. Notably, this methodology demonstrates a broad substrate scope, as primary/secondary benzamides are well tolerated, and this process might facilitate the development of one-pot transformations of amides. (Figure presented.).
- Luo, Zhongfeng,Wu, Hongxiang,Li, Yue,Chen, Yuwen,Nie, Jingyi,Lu, Siqi,Zhu, Yulin,Zeng, Zhuo
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p. 4117 - 4125
(2019/08/01)
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- Intramolecular O-arylation using nano-magnetite supported N-heterocyclic carbene-copper complex with wingtip ferrocene
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Nano-magnetite supported N-heterocyclic carbene-copper complex with wingtip ferrocene has been prepared via multi-step procedure. The complex has been characterized by various analytical techniques such as fourier transform infrared (FT-IR), fourier transform Raman (FT-Raman), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), transmission electron microscopy (TEM) and vibrating sample magnetometer (VSM) analysis. The catalytic activity of the complex has been exploited in intramolecular O-arylation of o-iodoanilides under heterogeneous conditions. The complex could be successfully recycled up to twelve consecutive cycles.
- Naikwade, Altafhusen,Jagadale, Megha,Kale, Dolly,Gajare, Shivanand,Bansode, Prakash,Rashinkar, Gajanan
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- (Phosphinito)aryl benzimidazole PCN pincer palladium(II) complexes: Synthesis, characterization and catalytic activity in C–H arylation of azoles with aryl iodides
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The PCN pincer Pd(II) complexes 4a–c with (phosphinito)aryl benzimidazole ligands were conveniently synthesized by one-pot phosphorylation/palladation reaction of a (2-benzimidazolyl)-containing m-phenol derivative 3. The three complexes were well characterized by spectroscopic methods, elemental analysis and their molecular structures were further determined by X-ray single-crystal diffraction. The Pd(II) center in each complex adopts a typical distorted-square-planar geometry. With a catalyst loading of 0.25–0.5 mol%, complex 4a could effectively catalyze C–H arylation of benzothiazole, benzoxazole and thiazole with various aryl iodides in the presence of CuI as a cocatalyst.
- Wang, Cong,Li, Yang,Lu, Beibei,Hao, Xin-Qi,Gong, Jun-Fang,Song, Mao-Ping
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p. 184 - 192
(2017/11/03)
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- Synthesis of N-heterocyclic carbene-PdCl-[(2-Pyridyl)alkyl carboxylate] complexes and their catalytic activities towards arylation of (benzo)oxazoles with aryl bromides
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Four well-defined N-heterocyclic carbene-PdCl-[(2-Pyridyl)alkyl carboxylate] complexes have been conveniently synthesized through bridge-cleavage reactions of [Pd(μ-Cl)(Cl)(NHC)]2 with (2-pyridyl)alkyl carboxylic acids [2-(pyridin-2-yl)acetic acid and 3-(pyridin-2-yl)propanoic acid]. The new complexes have been fully characterized by NMR, elemental analysis, HR-MS and X-ray single-crystal diffraction. The catalytic performance of the complexes was screened and the obtained palladium (II) complexes shown effective catalytic activities for direct arylation of (benzo)oxazoles with aryl bromides. Moreover, the 2-(pyridin-2-yl)acetate stabilized NHC–Pd complexes were more efficient than the 3-(pyridin-2-yl)propanoate stabilized NHC–Pd analogues. Further studies exhibited that 2-(pyridin-2-yl)acetate, as ancillary ligand, could easily decarboxylate and transform into 2-methylpyridine in the reaction condition.
- Chen, Wei,Yang, Jin
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- (N-heterocyclic carbene)PdCl(N-heterocyclic carboxylate) complexes: Synthesis and catalytic activities towards arylation of benzoxazoles with aryl halides
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A series of N-heterocyclic carboxylate-stabilized N-heterocyclic carbene palladium complexes have been synthesized and fully characterized. The solid-state structures indicate that each of the palladium centers is coordinated by an N-heterocyclic carbene, a chloride and a bidentate N,O-donor N-heterocyclic carboxylate ligand. The catalytic performance of the complexes was screened and the results revealed that the complexes exhibit moderate to high catalytic activities for the direct C─H bond arylation of benzoxazoles with aryl bromides.
- Yang, Jin
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- Direct C—H Bond Activation of Benzoxazole and Benzothiazole with Aryl Bromides Catalyzed by Palladium(II)-N-heterocyclic Carbene Complexes
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Herein, we report that a series of novel palladium(II)-NHC complexes (NHC=N-heterocyclic carbene) were synthesized. The structures of all novel complexes were characterized by 1H NMR, 13C NMR, FT-IR spectroscopy and elemental analysis techniques. These palladium(II)-NHC complexes were tested as efficient catalysts in the direct C—H bond activation of benzoxazole and benzothiazole with aryl bromides in the presence of 1 mol% catalyst loading at 150 °C for 4 h. Under the given conditions, various aryl bromides were successfully applied as the arylating reagents to achieve the 2-arylbenzoxazoles and 2-arylbenzothiazoles in acceptable to high yields.
- Kalo?lu, Murat,Kalo?lur, Nazan,?zdemir, ?smail
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p. 837 - 844
(2018/07/31)
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- Dibenzofuran and dibenzothiophene based palladium(ii)/NHC catalysts-synthesis and applications in C-C bond formation
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In the quest for a new ligand system for Pd(ii)/NHCs, we developed new dibenzofuran and dibenzothiophene based palladium N-heterocyclic carbene catalysts D1-D6 in good yields. All the catalysts were characterized by multinuclear NMR spectroscopy and HRMS. The X-ray crystal structure of the representative dibenzothiophene based Pd(ii)/NHC D4 was determined. Among the precatalysts, D1 was shown to be highly effective in the Suzuki-Miyaura cross-coupling reaction of heterocyclic bromides with boronic acids. Besides, D1 affords diverse arylated benzoxazoles via direct C-H bond functionalization with substituted bromo derivatives.
- Karthik, Shanmugam,Gandhi, Thirumanavelan
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supporting information
p. 15811 - 15819
(2018/10/04)
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- Heteroleptic palladium(II) complexes containing N-heterocyclic carbenes and 4-phenyl-1H-1,2,3-triazole: Synthesis, characterization, and catalytic application
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Reaction of the dimeric N-heterocyclic carbene (NHC) palladium compounds [Pd(μ-Cl)(Cl)(NHC)]2 with 4-phenyl-1H-1,2,3-triazole gave four mono- and dinuclear complexes 1–4. Mononuclear complexes 1 and 2 [(NHC)PdCl2(4-phenyl-1H-1,2,3-triazole)] were obtained when the reactions were performed in CH2Cl2, whereas dinuclear complexes 3 and 4 [Pd2(μ-Cl)(μ-4-phenyl-1H-1,2,3-triazole)Cl2(NHC)2] were obtained when the reactions were performed in THF in reflux with Et3N as the base. Further explorations of the catalytic properties of 1–4 for Pd-catalyzed transformations have been performed and these complexes exhibited moderate to high catalytic activities for Suzuki–Miyaura coupling and arylation of benzoxazoles with aryl bromides.
- Chen, Wei,Yang, Jin
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- Palladium(II) Immobilized Onto the Glucose Functionalized Magnetic Nanoparticle as a New and Efficient Catalyst for the One-pot Synthesis of Benzoxazoles
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Palladium(II) have been immobilized into the nano magnetic Fe3O4 which was functionalized with glucose in order to achieve a one-pot synthesis of 2-substituted benzoxazole derivatives with high yields in the diverse range of organic solvents. The nano catalyst is highly dispersive in polar solvents and can be easily recovered and reused for 6 runs without significant loss of its activity. Finally, the catalyst was fully characterized by FT-IR, TGA, CHN, SEM, EDX and atomic absorption spectroscopy.
- Moghaddam, Firouz Matloubi,Saberi, Vahid,Kalhor, Sepideh,Veisi, Nazila
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- Phosphonium acidic ionic liquid: An efficient and recyclable homogeneous catalyst for the synthesis of 2-Arylbenzoxazoles, 2-Arylbenzimidazoles, and 2-Arylbenzothiazoles
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A highly efficient and green strategy for the synthesis of 2-Arylbenzoxazoles, 2-Arylbenzimidazoles, and 2-Arylbenzothiazoles catalyzed by phosphonium acidic ionic liquid has been developed via the condensation of o-Aminophenol, o-phenylenediamines, and o-Aminothiophenol, respectively, with aldehydes. The reaction has a good yield, the broad substrate scope, and mild condition. Triphenyl(butyl-3-sulphonyl)phosphonium toluenesulfonate catalyst was easily obtained from cheap and available starting materials through a one-pot synthesis. Its structure was identified by 1H NMR, 13C NMR, 31P NMR, and FT-IR techniques. Other properties including thermal stability and acidity were determined by TGA and Hammett acidity function method. Interestingly, the catalyst can maintain its constantly outstanding performance till the fourth recovery.
- Nguyen, Quang The,Thi Hang, Anh-Hung,Ho Nguyen, Thuy-Linh,Nguyen Chau, Duy-Khiem,Tran, Phuong Hoang
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p. 11834 - 11842
(2018/04/05)
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- Oxidative NHC Catalysis for the Generation of Imidoyl Azoliums: Synthesis of Benzoxazoles
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N-Heterocyclic carbene (NHC)-catalyzed intramolecular cyclization of aldimines generated from 2-amino phenols and aromatic aldehydes leading to the synthesis of 2-arylbenzoxazoles under mild conditions is presented. The reaction proceeds via the generation of the aza-Breslow intermediates from imines and NHC, which under oxidative conditions form the key imidoyl azoliums and a subsequent intramolecular cyclization furnishes the product. The reaction tolerates a broad range of functional groups, and the products are formed in generally good yields.
- Patra, Atanu,James, Anjima,Das, Tamal Kanti,Biju, Akkattu T.
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p. 14820 - 14826
(2019/01/03)
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- Synthesis and characterization of a novel oxo-bridged binuclear iron(iii) complex: Its catalytic application in the synthesis of benzoxazoles using benzyl alcohol in water
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In the present work, the synthesis and characterization of a novel binuclear oxo-bridged iron(iii) complex, (FeLAPIP)2O, where LAPIP is the deprotonated form of a tetradentateo-aminophenol-iminopyridine ligand, is described. The iron complex was characterized using different techniques including X-ray crystallography, infrared spectroscopy, UV-Vis, magnetic susceptibility and cyclic voltammetry. The X-ray structure analysis revealed that in the structure of the (FeLAPIP)2O complex, each iron(iii) is coordinated in a distorted square pyramidal arrangement by an oxo group, three amine nitrogens and one oxygen atom of the o-aminophenolate ligand. The variable-temperature magnetic measurement exhibits strong antiferromagnetic coupling between two iron(iii) centers. Cyclic voltammetry measurements showed two kinds of quasireversible events, suggesting the formation of a phenoxyl radical species in the region of the anodic peaks and a metal-centered redox (FeIII/FeII) process at low potential. The catalytic activity of this Fe-complex was evaluated in coupling of 2-aminophenol and benzyl alcohols for the one-pot synthesis of benzoxazoles. The catalyst system showed high catalytic activity in this transformation and benzoxazole derivatives were obtained in good to excellent yields. tert-Butyl hydroperoxide was used as an oxidant and 1.2 mol% of catalyst was needed to accomplish the reaction in water as the green solvent.
- Safaei, Elham,Alaji, Zahra,Panahi, Farhad,Wojtczak, Andrzej,Jagli?i?, Janez Zvonko
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supporting information
p. 7230 - 7236
(2018/05/07)
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- A by bio-catalytic oxidation cyclized synthesis of 2 - substituted benzoxazole compound green method (by machine translation)
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The invention discloses a by bio-catalytic oxidation cyclized synthesis of 2 - substituted benzoxazole compound green method, which belongs to the technical field of biological catalytic synthesis, uses aldehyde and phenol amine or benzoxazole and cyclic secondary amine as the substrate of reaction, methylene chloride as the solvent, biological protein as a catalyst. Operation comprises the following steps first reaction to produce intermediate of the reaction substrate, then the hemoglobin, the oxidizing agent, the solvent is added in a reaction vessel, the reaction at room temperature under the condition of 2 hours. The experiment shows that, various types of hemoglobin and horse radish peroxidase and heme to said reaction have a catalytic effect, wherein the Vitreoscilla hemoglobin catalytic effect is the best, yield is up to 91%, superior to the traditional chemical synthesis method. The use of hemoglobin catalysts such as than the traditional chemical synthesis method more green environmental protection, is characterized in that: there are no harmful reagent to use, may be any metal ion catalysis, reduce the amount of the oxidizing agent and the catalyst. (by machine translation)
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Paragraph 0029; 0030; 0031
(2018/10/11)
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