5998-51-6Relevant articles and documents
2-Arylbenzoxazoles from phenolic Schiff's bases by thianthrene cation radical
Park, Koon Ha,Jun, Kun,Shin, Seung Rim,Oh, Sea Wha
, p. 8869 - 8870 (1996)
2-Arylbenzoxazoles 2 have been made in 91-97% yields from phenolic Schiff's bases 1 by thianthrene cation radical perchlorate (Th+.ClO4-) in the presence of 2,6-di-tert-butyl-4-methylpyridine. Copyright (C) 1996 Published by Elsevier Science Ltd.
Cu-Catalyzed Synthesis of Benzoxazole with Phenol and Cyclic Oxime
Wang, Zheng-Hai,Wang, Dong-Hui
supporting information, p. 782 - 785 (2022/01/20)
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.
Metal-Free Oxidative Condensation of Catechols, Aldehydes and NH4OAc towards Benzoxazoles
Dong, Jianyu,Geng, Furong,Su, Lebin,Wu, Shaofeng,Yin, Shuang-Feng,Zhou, Dan,Zhou, Yongbo
supporting information, p. 3607 - 3614 (2021/07/28)
Benzoxazoles extensively exist in biologically active compounds, natural products, pharmaceuticals and functional materials. Thus, facile and green synthesis of such valuable compounds from easily available substrates will make a contribution to drug, material, and fine chemistry. A method for the synthesis of benzoxazoles from catechols, aldehydes and ammonium acetate is developed using NaIO4 as oxidant under metal- and additive-free conditions. A broad range of benzoxazoles including some fluorescent whitening agents, JTP-426467 and tafamidis analogues are synthesized in 56–95% yields with outstanding functional group tolerance. Mechanistic investigations suggest that an interesting o-iminocyclohexa-diene alcohol intermediate is involved in the reaction. These salient features of the protocol make it an alternative for the synthesis of benzoxazoles. (Figure presented.).
Unsymmetrical Pincer N -Heterocyclic Carbene-Nitrogen-Phosphine Chelated Palladium(II) Complexes: Synthesis, Structure, and Reactivity in Direct Csp2-H Arylation of Benzoxazoles
Li, Yaqiu,Yu, Xiaojun,Wang, Yangdiandian,Fu, Haiyan,Zheng, Xueli,Chen, Hua,Li, Ruixiang
, p. 979 - 988 (2018/03/30)
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.
