- 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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- 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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- 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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- 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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- One-Pot, Borax-mediated synthesis of structurally diverse N, S-heterocycles in water
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Herein, a borax–mediated convenient and efficient strategy for the synthesis of prominent structurally diverse N, S-heterocycles such as quinazolin-4(3H)-one, benzothiadiazine 1,1-dioxide, benzothioazole, and benzoxazoles from readily available 2-aminobenzamide/2-aminobenzenesulfonamide/2-aminothiophenol/2-aminophenol with α,α,α-trihalotoluenes at 100 ℃ in water is elaborated. Upon using aldehydes instead of α,α,α-trihalotoluenes, the reactions proceed through domino fashion under the catalytic effect borax to yield 2,3-dihydroquinazolin-4(1H)-one, 3,4-dihydrothiadiazine 1,1-dioxide, and benzothiazoles in one-pot at 60 ℃. The advantages of this protocol are practical simplicity, large substrate scope, moderate to excellent yields, and the use of water as the solvent.
- Rao, Mugada Sugunakara,Hussain, Sahid
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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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-
- Sulfur-Promoted Synthesis of Benzoxazoles from 2-Aminophenols and Aldehydes
-
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
-
supporting information
p. 3818 - 3821
(2020/06/10)
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- Consecutive Oxidation/Condensation/Cyclization/Aromatization Sequences Catalyzed by Nanostructured Iron(III)-Porphyrin Complex towards Benzoxazole Derivatives
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A facile, efficient, and eco-friendly strategy to access benzoxazole heterocyclic products has been accomplished through oxidation of catechols followed by condensation/cyclization/aromatization sequences. This process is catalyzed by nanostructured iron(III)-porphyrin complex to form desired benzoxazole derivatives at room temperature under air condition. The procedure is widely applicable to diverse amines, and can provide the heterocyclic products in a scalable fashion, as well. One of the most significant types of oxidizing agents in nature is the iron-porphyrin complexes (0.1 mol-%), existing in the structure of hemoglobin. They have benefits such as low toxicity and high oxidation potential for many substrates.
- Aberi, Mahdi,Aboonajmi, Jasem,Sharghi, Hashem,Shiri, Pezhman
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p. 5978 - 5984
(2020/10/02)
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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
-
supporting information
p. 1687 - 1694
(2020/05/25)
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- One-pot multicomponent reaction of catechols, ammonium acetate, and aldehydes for the synthesis of benzoxazole derivatives using the fe(iii)-salen complex
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The Fe(III)-salen complex has been applied successfully as a catalyst for the novel, simple, efficient, and one-pot multicomponent synthesis of benzoxazole derivatives from catechols, ammonium acetate as the nitrogen source, and aldehydes (nontoxic and cheap alternatives of amines) for the first time. Using this procedure, a wide range of benzoxazoles was successfully synthesized in the presence of a catalyst in EtOH under mild conditions, and all products were obtained in excellent yields. To the best of our knowledge, this method is the first example of the multicomponent synthesis of benzoxazole derivatives using these starting materials. The notable features such as the use of air that is considered as a benign oxidant and EtOH as a green solvent, ease of product separation, readily available and inexpensive aldehydes, and mild conditions make our procedure more efficient and practical for organic synthesis. Moreover, the current protocol is successfully applied to synthesize desirable products on a large scale.
- Sharghi, Hashem,Aboonajmi, Jasem,Aberi, Mahdi
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p. 6567 - 6577
(2020/06/08)
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- Synthesis of substituted benzo[: B] [1,4]oxazepine derivatives by the reaction of 2-aminophenols with alkynones
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We have developed a novel synthetic method accessing benzo[b][1,4]oxazepines that are one of the rare classes of benzoxazepine derivatives by reaction of 2-aminophenols with alkynones in 1,4-dioxane at 100 °C. A series of benzo[b][1,4]oxazepine derivatives can be prepared by using this synthetic protocol. Mechanistic experiments indicated that the hydroxy proton of the aminophenol could play a crucial role in the formation of an alkynylketimine intermediate that undergoes 7-endo-dig cyclization.
- Oshimoto, Kohei,Zhou, Biao,Tsuji, Hiroaki,Kawatsura, Motoi
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p. 415 - 419
(2020/01/30)
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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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- 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
-
supporting information
p. 1299 - 1303
(2020/08/05)
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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)
- -
-
Paragraph 0044-0051; 0058-0061; 0063-0067; 0068-0071
(2020/06/05)
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- Preparation method of 2-benzooxazole compound
-
The invention relates to a preparation method of a 2-phenylbenzoxazole compound. The structural formula of the prepared 2-phenylbenzoxazole compound is shown in Figure 1, wherein R1, R2, R3, R4, R5, R6, R7, R8 and R9 are a hydrogen atom, an alkyl group, an alkoxy group, halogen and trifluoromethyl. The preparation method is as follows: a phenolic compound, a diketone compound, alkali and a solvent are blended under room temperature to 200 DEG C for 1 to 24 hours; after reaction is complete, quenching is carried out, organic solvent extraction, concentration and purification are carried out, so that the 2-phenylbenzoxazole compound is obtained, and the yield is 37 to 78 percent. The preparation method has the characteristics of easy material obtainment, mild reaction condition, short reaction time, simplicity in operation and the like.
- -
-
Paragraph 0013
(2019/12/25)
-
- 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
-
supporting information
p. 7506 - 7510
(2019/11/28)
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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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- 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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- 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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- 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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- Sulfur-Catalyzed Oxidative Coupling of Dibenzyl Disulfides with Amines: Access to Thioamides and Aza Heterocycles
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In the presence of catalytic amounts of elemental sulfur, dibenzyl disulfide/DMSO was found to be an excellent thiobenzoylating agent of amines to provide a wide range of thioamides. The reaction becomes autocatalytic when anilines substituted by an o-cyclizable group were used as nucleophile, leading to the corresponding 2-aryl aza heterocycles. (Figure presented.).
- Nguyen, Thanh Binh,Nguyen, Le Phuong Anh,Nguyen, Thi Thu Tram
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supporting information
p. 1787 - 1791
(2019/02/26)
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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.
- -
-
Paragraph 0062; 0091
(2019/01/21)
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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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- 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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- N-Heterocyclic Carbene (NHC)-Catalyzed One-Pot Aerobic Oxidative Synthesis of 2-Substituted Benzo[ d ]oxazoles, Benzo[ d ]thiazoles and 1,2-Disubstituted Benzo[ d ]imidazoles
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N-Heterocyclic carbene (NHC), generated in situ from easily available N-heterocyclic imidazolium salt with air as terminal oxidant, has successfully been utilized as a cheap and efficient catalyst for one-pot aerobic oxidative synthesis of 2-arylbenzo[ d ]oxazoles, 2-substituted benzo[ d ]thiazoles, and 1,2-disubstituted benzo[ d ]imidazoles.
- Zhou, Quan,Liu, Shu,Ma, Ming,Cui, He-Zhen,Hong, Xi,Huang, Shuang,Zhang, Jing-Fan,Hou, Xiu-Feng
-
supporting information
p. 1315 - 1322
(2018/03/10)
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- Unexpected Decarboxylation-Triggered o-Hydroxyl-Controlled Redox Condensation of Phenylglycines with 2-Nitrophenols in Aqueous Media
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A decarboxylation-triggered and o-hydroxyl-controlled hydrogen-transfer strategy for the one-pot synthesis of benzoxazoles from readily available amino acids and 2-nitrophenols is reported. On the basis of this autoredox reaction, the C?N bond can be efficiently constructed to afford the desired products in moderate to good yields under transition-metal-free conditions in aqueous media. (Figure presented.).
- Tang, Lin,Yang, Zhen,Sun, Tian,Zhang, Di,Ma, Xiantao,Rao, Weihao,Zhou, Yuqiang
-
supporting information
p. 3055 - 3062
(2018/08/01)
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- Iron-Catalyzed Sulfur-Promoted Decyanative Redox Condensation of o-Nitrophenols and Arylacetonitriles: An Unprecedented Route to 2-Arylbenzoxazoles
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Elemental sulfur in the presence of a catalytic amount of FeCl2·4H2O was found to be highly efficient for the promotion of decyanative redox condensation reactions of o-nitrophenols with arylacetonitriles, to give a wide range of 2-arylbenzoxazoles. The utility of elemental sulfur was highlighted by its role as cyanide scavenger and external reducing agent.
- Nguyen, Thanh Binh,Lung, Jerome Cheung
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supporting information
p. 5815 - 5818
(2018/11/24)
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- Unsymmetrical Pincer N -Heterocyclic Carbene-Nitrogen-Phosphine Chelated Palladium(II) Complexes: Synthesis, Structure, and Reactivity in Direct Csp2-H Arylation of Benzoxazoles
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An unsymmetrical pincer N-heterocyclic carbene-nitrogen-phosphine (CNP) and its palladium complexes PdCl2(κ2-CP) (4) and [PdCl(κ3-CNP)]PF6 (5·PF6) were synthesized. NMR spectra disclosed that the transformation of complex 4 structure occurred in the solution. Further NMR experimental and single crystal structure analysis of complex 4 provided unequivocal and structural evidence for the formation of complex [PdCl(κ3-CNP)]Cl (5·Cl) in the solution of complex 4. The catalytic performance of palladium complexes 4 and 5·PF6 was investigated with the direct Csp2-H arylation of benzoxazoles with aryl bromides. Notably, aryl bromides could give up to 97% arylation products in the presence of 0.5% complex 4. For ortho-substituted substrates, the steric hindrance had a significant impact, but product yields could be improved remarkably by extending reaction time. This result implied the catalytic active species in this system was stable and kept in a long lifetime. The flexible backbone and unsymmetrical pincer structure with a flank N-heterocyclic carbine should be a feasible strategy to realize an efficient catalytic transformation. This simple catalyst system first realized the direct arylation of aryl bromides with a catalyst loading as low as 0.25% without excessive base and copper as assistant catalyst.
- Li, Yaqiu,Yu, Xiaojun,Wang, Yangdiandian,Fu, Haiyan,Zheng, Xueli,Chen, Hua,Li, Ruixiang
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p. 979 - 988
(2018/03/30)
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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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- Deep eutectic solvent-catalyzed arylation of benzoxazoles with aromatic aldehydes
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A novel and efficient methodology for the arylation of benzoxazoles with aromatic aldehydes catalyzed by deep eutectic solvent has been developed. The reaction smoothly proceeded with a wide range of substrates to give the desired products in high yields within short reaction time. Deep eutectic solvents are easily recovered and reused without significant loss of catalytic activity.
- Tran, Phuong Hoang,Thi Hang, Anh-Hung
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p. 11127 - 11133
(2018/03/26)
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- A benzoxazole for the arylation method (by machine translation)
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The invention relates to a benzoxazole for the arylation method, comprises the following steps: under the protection of the inert gas, the benzoxazole, aryl/heteroaryl tosylates, catalyst nitrogen heterocyclic carbene - palladium complex, alkaline material, reaction solvent, in the 80 - 150 °C reaction 12 - 24 H of the reaction liquid obtained, then processing reaction liquid to obtain product, to obtain 2 - aryl benzoxazole. The invention discloses a benzoxazole for the arylation method development of novel catalytic system, catalyst stability, is easy to obtain, can make the stable, low price of the aryl/heteroaryl tosylates participate in the reaction, reaction operation is simple, low cost, product yield and purity and the like, has good value for research and industrial application produces the scenery. (by machine translation)
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-
Paragraph 0071; 0080
(2018/11/03)
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- Oxidative Synthesis of Benzimidazoles, Quinoxalines, and Benzoxazoles from Primary Amines by ortho-Quinone Catalysis
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The bioinspired ortho-quinone catalysts have been applied to heterocycles synthesis. Without any metal cocatalysts, a sole ortho-quinone catalyst enables the oxidative synthesis of benzimidazoles, quinoxalines and benzoxazoles from primary amines in high yields under mild conditions with oxygen as the terminal oxidant.
- Zhang, Ruipu,Qin, Yan,Zhang, Long,Luo, Sanzhong
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supporting information
p. 5629 - 5632
(2017/10/25)
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- A new superacid hafnium-based metal-organic framework as a highly active heterogeneous catalyst for the synthesis of benzoxazoles under solvent-free conditions
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A new crystalline porous superacid material was prepared by sulfation of a Hf-MOF constructed from a 6-connected Hf node and 1,3,5-benzenetricarboxylate. The new superacid MOF with the presence of sulfate groups coordinated to a Hf-oxo cluster as superacid sites was found to be an effective heterogeneous catalyst for solvent-free heterocyclization for benzoxazole synthesis.
- Nguyen, Linh H.T.,Nguyen, The T.,Nguyen, Ha L.,Doan, Tan L.H.,Tran, Phuong Hoang
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p. 4346 - 4350
(2017/10/13)
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- Preparation method of 2-aryl benzoxazole and 2-aryl benzothiazole compounds
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The invention belongs to the technical field of organic synthesis, and in particular relates to a preparation method of 2-aryl benzoxazole and 2-aryl benzothiazole compounds. According to the invention, 2-aminophenol(2-aminothiophenol) and aromatic aldehydes are stirred at the temperature of 100 to 130 DEG C, imidazolium salt of which the molar equivalent amount is 10% to 20% and K2CO3 of which the molar equivalent amount is 25% to 50% are added, air is used as an oxidant, and then 2-aryl benzoxazole and 2-aryl benzothiazole compounds are synthesized by a reaction. According to the invention, the cheap and easily prepared imidazolium salt is taken as a catalyst and the cheap air is taken as the oxidant to synthesize target products in a high yield, so that the preparation method of the 2-aryl benzoxazole and 2-aryl benzothiazole compounds is greatly lowered in production cost and capable of adapting to the industrial application to a greater extent.
- -
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Paragraph 0012; 0013
(2017/08/29)
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- Synthesis of Benzoxazoles Using Electrochemically Generated Hypervalent Iodine
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The indirect ("ex-cell") electrochemical synthesis of benzoxazoles from imines using a redox mediator based on the iodine(I)/iodine(III) redox couple is reported. Tethering the redox-active iodophenyl subunit to a tetra-alkylammonium moiety allowed for anodic oxidation to be performed without supporting electrolyte. The mediator salt can be easily recovered and reused. Our "ex-cell" approach toward the electrosynthesis of benzoxazoles is compatible with a range of redox-sensitive functional groups. An unprecedented concerted reductive elimination mechanism for benzoxazole formation is proposed on the basis of control experiments and DFT calculations.
- Koleda, Olesja,Broese, Timo,Noetzel, Jan,Roemelt, Michael,Suna, Edgars,Francke, Robert
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p. 11669 - 11681
(2017/11/24)
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- OMS-2/H2O2/Dimethyl Carbonate: An Environmentally-Friendly Heterogeneous Catalytic System for the Oxidative Synthesis of Benzoxazoles at Room Temperature
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A manganese octahedral molecular sieve (OMS-2) was found to be an efficient and recyclable heterogeneous catalyst for the oxidative synthesis of benzoxazoles in the gram-scale from phenolic imines at room temperature. H2O2 and biobased reagent dimethyl carbonate (DMC) were successfully employed as the environmentally friendly oxidant and solvent, respectively, in an OMS-2-catalysted redox reaction for the first time. Benzoxazoles could also be obtained from N-substituted 2-aminophenols via Cu(OH)x/OMS-2-catalyzed sequential oxidative transformation at elevated temperatures.
- Meng, Xu,Wang, Yuanguang,Chen, Baohua,Chen, Gexin,Jing, Zhenqiang,Zhao, Peiqing
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p. 2018 - 2024
(2017/12/26)
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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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- Method for preparing benzoxazole compound by heterogeneous catalytic oxidation
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The invention discloses a method for preparing a benzoxazole compound by heterogeneous catalytic oxidation. The method comprises the following steps: mixing phenolic Schiff base, an OMS-2 type manganese oxide octahedral molecular sieve, an oxidant and carbonic esters and reacting to obtain the benzoxazole compound, wherein structures of the phenolic Schiff base and the benzoxazole compound are respectively shown as formulas I and II: the formula I is shown in the description and the formula II is shown in the description, wherein R can be selected from hydrogen, alkyl, alkoxyl, hydroxyl, an ester group, a carboxylic group or halogen; R can be selected from alkyl, aryl and alkenyl. According to the method disclosed by the invention, a green catalytic reaction system which is composed of a heterogeneous catalyst OMS-2 type manganese oxide molecular sieve, a green oxidant H2O2 and a green medium carbonate and has a long service life and is cheap is adopted, so that an acid-alkali additive can be avoided; the catalyst has high activity and a long service life; the method disclosed by the invention is simple to operate and has moderate reaction conditions; new three wastes are not generated and the method is clean and environmentally friendly; the solvent treatment cost can be reduced and the conversion rate of reactants and the yield of a target product are improved, so that the method can be more adaptive to industrial application to the greater extent.
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Paragraph 0041; 0042
(2017/10/28)
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- Nickel-catalyzed C?H arylation of benzoxazoles and oxazoles: Benchmarking the influence of electronic, steric and leaving group variations in phenolic electrophiles
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Electronic, steric and leaving group effects for Ni-catalyzed direct arylations using C?O electrophiles were benchmarked. The scope of arylations with pivalates was general with respect to both the electronics on the electrophile and the azoles. Furthermore, the arylation of azoles with tosylates, mesylates and carbamates with varying electronics was explored, and showed electronic trends similar to those of the pivalate reactions. Finally, the relative rate of arylation of 5-methyl benzoxazole with two electronically-similar electrophiles bearing different leaving groups was established. The results from these studies implicate the following order of relative reactivity: mesylates>pivalates>carbamates.
- Steinberg, Deborah F.,Turk, Morgan C.,Kalyani, Dipannita
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supporting information
p. 2196 - 2209
(2017/03/24)
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- p-Toluenesulfonic acid-catalyzed metal-free formal [4?+?1] heteroannulation via N[sbnd]H/O[sbnd]H/S[sbnd]H functionalization: One-pot access to 2-aryl/hetaryl/alkyl benzazole derivatives
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A concise and direct one-pot [4?+?1] synthetic strategy for the construction of 2-substituted benzazoles such as benzoxazoles and benzothiazoles has been disclosed in high yields (80–98%) by cascade coupling reaction of 2-amino(thio)phenols with β-oxodithioesters. The current approach enables N[sbnd]H/O[sbnd]H/S[sbnd]H functionalization in one-pot under solventless condition leading to diverse benzazoles without use of any external metal. A wide range of 2-amino(thio)phenols and β-oxodithioesters are compatible toward this transformation with excellent functional group tolerance. Furthermore, we preempt the wider implications of this novel strategy by demonstrating its compatibility toward versatile diversification of DNA Topoisomerase-II inhibitors.
- Srivastava, Abhijeet,Shukla, Gaurav,Singh, Maya Shankar
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p. 879 - 887
(2017/01/25)
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- Atom economic palladium catalyzed novel approach for arylation of benzothiazole and benzoxazole with triarylbismuth reagents via C[sbnd]H activation
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We have developed a novel method for the direct C[sbnd]H functionalization of benzothiazole and benzoxazole using triarylbismuth reagents. The arylation proceeds using the homogeneous catalytic system PdCl2, Cu(OAc)2 and PPh3 ligand. Triarylbismuthines, which act as threefold arylating reagents, have low toxicity, are green and ecofriendly. These methodologies are particularly useful to prepare arylated benzothiazoles and benzoxazoles.
- Balsane, Kishor Eknath,Gund, Sitaram Haribhau,Nagarkar, Jayashree Milind
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- Environmental benign synthesis of novel double layered nano catalyst and their catalytic activity in synthesis of 2-substituted benzoxazoles
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Synthesis of Cu-Al hydrotalcite by co precipitation method is being described. Synthesized nano catalyst has been characterized by powder X-ray diffraction, scanning electron microscopy, FT-IR and thermogravimetric analyses which confirm hydrotalcite-like structure. Effect of molar concentration, catalyst loading, reaction time and catalytic activity have been investigated in the synthesis of benzoxazoles under solvent free conditions using 2-amino phenol and benzoyl chloride. The influence of the hydrotalcite and their different amounts on reactivity was studied. Catalyst can be recycle and used for further reaction without losing its activity.
- Gupta, Ruchi,Sahu, Pramod K.,Sahu, Praveen K.,Srivastava,Agarwal
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p. 119 - 123
(2017/01/25)
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- Copper-catalyzed synthesis of benzoxazoles: Via tandem cyclization of 2-halophenols with amidines
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This work reports a simple, efficient and alternative synthetic route for the preparation of benzoxazoles via tandem cyclization of 2-halophenols with amidines. The developed methodology is free from ligands and uses inexpensive and easily available CuCl as a catalyst. This protocol avoids the use of any oxidant or inorganic acids. Various benzoxazole derivatives were synthesized in good to excellent yields. To the best of our knowledge, this is the first time that the synthesis of benzoxazoles from 2-halophenols with both aromatic and aliphatic amidines is reported. Owing to the simplicity of this protocol, the preparation of benzoxazoles could be achieved at a gram scale level.
- Tiwari, Abhishek R.,Bhanage, Bhalchandra M.
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p. 7920 - 7926
(2016/08/30)
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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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- S8-Mediated Cyclization of 2-Aminophenols/thiophenols with Arylmethyl Chloride: Approach to Benzoxazoles and Benzothiazoles
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A metal-free approach to benzazoles from arylmethyl chlorides and 2-mercaptan/2-hydroxyanilines using elemental sulfur as a traceless oxidizing agent has been developed. The reactions proceeded in good to excellent yields, exhibiting good functional groups tolerance and gram-scale ability. A key mechanistic investigation indicated that the key intermediate trisulfide 6, which was characterized by NMR, HRMS and crystal X-ray crystallography, was separated in the reaction prior to the formation of the product.
- Gan, Haifeng,Miao, Dazhuang,Pan, Qiang,Hu, Renhe,Li, Xiaotong,Han, Shiqing
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supporting information
p. 1770 - 1774
(2016/07/07)
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- Chelating palladium complexes containing pyridine/pyrimidine hydroxyalkyl di-functionalized N-heterocyclic carbenes: Synthesis, structure, and catalytic activity towards C-H activation
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The synthesis of novel chelating palladium complexes containing pyridine/pyrimidine hydroxyalkyl di-functionalized N-heterocyclic carbenes (NHCs) via direct metallation of the precursor imidazolium salts is presented. The structure has been characterized unambiguously by X-ray single crystal analysis. Catalytic activity investigation showed that the complexes catalyse the direct C-H bond arylation of (benzo)oxazoles efficiently when using tBuOLi as base and DMF as solvent.
- Yang, Liangru,Yuan, Jinwei,Mao, Pu,Guo, Qi
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p. 107601 - 107607
(2016/01/08)
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- One-pot synthesis of benzoxazoles via the metal-free ortho-C-H functionalization of phenols with nitroalkanes
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PPA-activated nitroalkanes are employed in the design of a one-pot cascade transformation involving metal-free and oxidant-free direct ortho-C-H functionalization, followed by Beckman rearrangement and intramolecular cyclocondensation to produce benzoxazoles and benzobisoxazoles directly from easily available phenols.
- Aksenov, Nicolai A.,Aksenov, Alexander V.,Nadein, Oleg N.,Aksenov, Dmitrii A.,Smirnov, Alexander N.,Rubin, Michael
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p. 71620 - 71626
(2015/09/08)
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- Iron(II) bromide-catalyzed oxidative coupling of benzylamines with ortho-substituted anilines: Synthesis of 1,3-benzazoles
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An iron(II) bromide-catalyzed oxidative coupling of benzylamines with 2-amino/hydroxy/mercapto-anilines has been developed, allowing the synthesis of a diversity of substituted 1,3-benzazoles in good to excellent yields. This transformation is compatible with a wide range of functional groups. The method is practical, economical and employs molecular oxygen as an oxidant.
- Gopalaiah, Kovuru,Chandrudu, Sankala Naga
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p. 5015 - 5023
(2015/03/03)
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- Copper-catalyzed synthesis of 2-arylbenzoxazoles from o-aminophenol derivatives with arylmethyl chlorides
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A facile and efficient synthesis of 2-arylbenzoxazoles via copper-catalyzed tandem condensation/oxidative reaction of o-aminophenol derivatives with arylmethyl chlorides was developed. Note that this reaction utilized arylmethyl chlorides as a new type of simple and cheap acyl sources and KNO3 as a readily available and low-cost benign oxidant.
- Zhang, Guodong,Wang, Peng,Yang, Fan,Wu, Yangjie
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supporting information
p. 57 - 63
(2015/02/02)
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- Palladium catalyzed Csp2-H activation for direct aryl hydroxylation: The unprecedented role of 1,4-dioxane as a source of hydroxyl radicals
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A novel strategy for direct aryl hydroxylation via Pd-catalysed Csp2-H activation through an unprecedented hydroxyl radical transfer from 1,4-dioxane, used as a solvent, is reported with bio relevant and sterically hindered heterocycles and various acyclic functionalities as versatile directing groups.
- Seth, Kapileswar,Nautiyal, Manesh,Purohit, Priyank,Parikh, Naisargee,Chakraborti, Asit K.
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p. 191 - 194
(2015/01/09)
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