- Cu-Catalyzed Synthesis of Benzoxazole with Phenol and Cyclic Oxime
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A Cu-catalyzed straightforward synthesis of benzoxazoles from free phenols and cyclic oxime esters is reported. The mild reaction conditions tolerate various electron-withdrawing and electron-donating functional groups on both substrates, affording benzoxazoles in moderate to good yields. With this protocol, large-scale syntheses of Ezutromid and Flunoxaprofe in one or two steps are demonstrated. A catalytic mechanism, which includes Cu-catalyzed amination via inner-sphere electron transfer and consequent annulation, is proposed.
- Wang, Zheng-Hai,Wang, Dong-Hui
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supporting information
p. 782 - 785
(2022/01/20)
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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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- 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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- Liebeskind-Srogl-type cross-coupling reaction of azole-2-thiones with triarylbismuthines: Synthesis of 2-arylazoles
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Liebeskind-Srogl-type C(HetAr)–C(Ar) bond formation using trivalent organobismuth compounds as a new class of arylating reagents is described. The reaction of benzazole-2-thiones with triarylbismuthines in the presence of 10 mol% Pd(dba)2 and 2.0 equiv. Cu(OAc)2 at 80 °C affords 2-arylbenzothiazoles, benzoxazoles, and N-methyl benzimidazole in moderate-to-high yield. The reaction is sensitive to the electronic nature of triarylbismuthines: compounds bearing an electron-withdrawing group on the phenyl ring showed higher reactivity than those having an electron-donating group.
- Murata, Yuki,Terazoe, Aki,Kiba, Misato,Kitamura, Yuki,Matsumura, Mio,Yasuike, Shuji
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supporting information
(2020/07/03)
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- α-d-Galacturonic Acid as Natural Ligand for Selective Copper-Catalyzed N-Arylation of N-Containing Heterocycles
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The first application of α-d-galacturonic acid hydrate (GalA) is reported here, as a potential O-donor ligand. The C-N couplings of N-heterocycles with aryl halides or arylboronic acids could be readily conducted and exhibited good functional group tolerance with characters of selectivity. These N-Arylazoles allow rapid access to several pharmaceutical intermediates and can be easily transformed into a variety of other interesting scaffolds as well.
- Yuan, Chunling,Zhao, Yingdai,Zheng, Li
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p. 2173 - 2180
(2019/11/25)
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- Iridium-catalyzed intramolecular C–N and C–O/S cross-coupling reactions: Preparation of benzoazole derivatives
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The irdium-catalyzed intramolecular arylcarbon-hetero cross-coupling reactions with o-haloarylamides or o-haloarylamidine have been effectively achieved using KOAc and just 1 mol% catalyst. The [Ir(cod)Cl]2 was proved to be more potential for smoothly assembling functional structures benzimidazoles, benzoxazoles and benzothiazoles, which was superior to Cu- and Pd-catalyzed systems. Simultaneously, a concise and efficient synthesis of tafamidis was developed in 5-g scale.
- Shi, Yajie,Zhou, Qifan,Du, Fangyu,Fu, Yang,Du, Yang,Fang, Ting,Chen, Guoliang
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supporting information
(2019/09/10)
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- Synthesis of benzoxazoles via the copper-catalyzed hydroamination of alkynones with 2-aminophenols
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We describe herein the synthetic method to benzoxazole derivatives via the copper-catalyzed hydroamination of alkynones with 2-aminophenols. The method produced a wide variety of functionalized benzoxazole derivatives in good yields. Preliminary mechanistic experiments revealed that the reaction would proceed through the copper-catalyzed hydroamination of alkynones and the sequential intramolecular cyclization of β-iminoketones/elimination of acetophenone promoted by the copper catalyst.
- Oshimoto, Kohei,Tsuji, Hiroaki,Kawatsura, Motoi
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p. 4225 - 4229
(2019/05/10)
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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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- Base-Free Selective O-Arylation and Sequential [3,3]-Rearrangement of Amidoximes with Diaryliodonium Salts: Synthesis of 2-Substituted Benzoxazoles
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A variety of functionalized 2-substituted benzoxazoles can be prepared in good yields from amidoximes and diaryliodonium salts by selective O-arylation and sequential [3,3]-rearrangement under metal-free conditions. O-arylation of amidoximes was promoted by 3 ? molecule sieves in the absence of a base and a sequential TFA-mediated [3,3]-rearrangement was used to synthesize 2-substituted benzoxazoles. Both of the O-aryl products and rearrangement products were compatible with a broad range of sensitive functional groups such as ester, aldehyde, nitro, vinyl, amine, and amide groups in addition to halides. A bidentate N-ligand with double benzoxazoles was prepared at gram-scale in two steps. (Figure presented.).
- Shi, Wei-Min,Li, Xiao-Hua,Liang, Cui,Mo, Dong-Liang
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p. 4129 - 4135
(2017/12/15)
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- 2-substituted benzoxazole preparation method of compound
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The invention relates to a preparing method of 2-substituted benzoxazole compounds. The compounds are obtained by reaction of products obtained by reaction of acyl chloride and o-nitrophenol or derivatives thereof under catalyzing of reducing agent ammonium formate, a solvent and palladium-containing agents. According to the method, the reaction condition is mild, environment is protected, raw materials are rich and easy to obtain, operation is easy, yield is high, and various kinds of performance are optimized.
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- Magnetic copper ferrite nanoparticles: An inexpensive, efficient, recyclable catalyst for the synthesis of substituted benzoxazoles via ullmann-type coupling under ligand-free conditions
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A new sustainable strategy for the synthesis of benzoxazoles from substituted N-(2-halophenyl)benzamides was developed in which inexpensive, readily available, air-stable, recyclable copper(II) ferrite serves as a nanocatalyst. The nanocatalyst can be completely recovered with an external magnet and can be used seven times without significant loss of catalytic activity. Georg Thieme Verlag Stuttgart. New York.
- Yang, Daoshan,Zhu, Xiao,Wei, Wei,Jiang, Min,Zhang, Ning,Ren, Dandan,You, Jinmao,Wang, Hua
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supporting information
p. 729 - 735
(2014/04/03)
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- Palladium-catalyzed direct arylation of benzoxazoles with unactivated simple arenes
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Using CuBr2 as an additive, the Pd-catalyzed intermolecular C-H-C-H cross-coupling between benzoxazoles and unactivated simple arenes has been developed. This protocol provides a straightforward approach for the biological activity of 2-arylbenzoxazole derivatives.
- Wu, Ge,Zhou, Jun,Zhang, Min,Hu, Peng,Su, Weiping
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supporting information
p. 8964 - 8966
(2012/11/14)
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- Facile and efficient synthesis of benzoxazoles and benzimidazoles: The application of Hantzsch ester 1,4-dihydropyridines in reductive cyclization reactions
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Both benzoxazole and benzimidazole are common heterocyclic scaffolds in biologically active and medicinally significant compounds. Reductive cyclization of ortho-substituted nitrobenzene derivatives provides an attractive route to benzoxazole or benzimidazole ring formation. Unfortunately, only a few synthetic methods by reductive cyclization ofortho-nitro compounds have been reported and the yields are rather low. In continuation of the development of biomimetic reductants in synthetically useful organic transformations, Hantzsch ester 1,4-dihydropyridine (HEH), analogues of NAD(P)H, has attracted a considerable amount of attention. Hence, we wish to report that benzoxazoles and benzimidazoles can be efficiently synthesized by the reaction of ortho-substituted nitrobenzene derivatives with HEH catalyzed by Pd/C. A range of functionalized ortho-nitrophenyl esters or ortho-nitrophenyl amides were efficiently reduced by HEH and cyclized to the corresponding benzoxazoles or benzimidazoles. Especially, working in the presence of the same substituents, benzimidazoles could be obtained in higher yields with respect to the corresponding benzoxazoles. Moreover, in the present work, the recycling of Pd/C was studied and was shown to maintain its high catalytic activity over five runs. On the basis of our experimental results and DFT calculations, a plausible reaction mechanism was proposed. Copyright
- Xing, Rui-Guang,Li, Ya-Nan,Liu, Qiang,Meng, Qing-Yuan,Li, Jing,Shen, Xiao-Xia,Liu, Zhengang,Zhou, Bo,Yao, Xiaojun,Liu, Zhong-Li
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experimental part
p. 6627 - 6632
(2011/03/17)
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- Parallel synthesis of a library of benzoxazoles and benzothiazoles using ligand-accelerated copper-catalyzed cyclizations of ortho-halobenzanilides
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A general method for the formation of benzoxazoles via a copper-catalyzed cyclization of ortho-haloanilides is reported. This approach complements the more commonly used strategies for benzoxazole formation which require 2-aminophenols as substrates. The reaction involves an intramolecular C-O cross-coupling of the ortho-haloanilides and is believed to proceed via an oxidative insertion/reductive elimination pathway through a Cu(I)/Cu(III) manifold. The reaction is also applicable to the formation of benzothiazoles. A variety of ligands including 1,10-phenanthroline and N,N′- dimethylethylenediamine were shown to provide ligand acceleration/stabilization in the reaction. Optimal conditions for cyclization used a catalyst combination of CuI and 1,10-phenanthroline (10 mol %). The method was amenable to a parallel-synthesis approach, as demonstrated by the synthesis of a library of benzoxazoles and benzothiazoles substituted at various positions in the ring. Most examples utilized the cyclization of ortho-bromoanilides, but orthoiodoanilides and ortho-chloroanilides also undergo a reaction under these conditions. The rate of reaction of the ortho-haloanilides follows the order I > Br > Cl, consistent with oxidative addition being the rate-determining step.
- Evindar, Ghotas,Batey, Robert A.
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p. 1802 - 1808
(2007/10/03)
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- A domino copper-catalyzed C-N and C-O cross-coupling for the conversion of primary amides into benzoxazoles
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Benzoxazoles can be efficiently prepared in a single step and in good yield from primary amides and o-dihalobenzenes using Cu catalysis. Starting from substituted o-bromochlorobenzenes this unusual domino reaction allows the regioselective formation of benzoxazoles.
- Altenhoff, Gereon,Glorius, Frank
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p. 1661 - 1664
(2007/10/03)
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