Synthesis of 2-substituted pyrimidines and benzoxazoles via a visible-light-driven organocatalytic aerobic oxidation: enhancement of the reaction rate and selectivity by a base
作者:Lin Wang、Zhi-Gang Ma、Xiao-Jing Wei、Qing-Yuan Meng、Deng-Tao Yang、Shao-Fu Du、Zi-Fei Chen、Li-Zhu Wu、Qiang Liu
DOI:10.1039/c4gc00337c
日期:——
An efficient visible-light-driven photocatalytic oxidation of various 2-substituted dihydropyrimidines and phenolic imines has been achieved using an organic photocatalyst eosin Y bis(tetrabutyl ammonium salt) (TBA-eosin Y) and inexpensive oxidant molecular oxygen. With the aid of a base, significantly enhanced photoinduced electron transfer from substrates dihydropyrimidines or phenolic imines to the excited state of TBA-eosin Y has enabled the aerobic oxidation to yield 2-(methylthio)pyrimidines or 2-arylbenzoxazoles selectively.
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.
Copper-catalyzed synthesis of benzoxazoles via tandem cyclization of 2-halophenols with amidines
作者:Abhishek R. Tiwari、Bhalchandra M. Bhanage
DOI:10.1039/c6ob01264g
日期:——
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 freefrom 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
An acid-mediated selective cleavage of C–C doublebond 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 doublebond of N-(2-hydroxylphenyl)enaminone is also realized using NCS
Metal-free direct annulation of 2-aminophenols and 2-aminothiophenols with unactivated amides through transamidation: Access to polysubstituted benzoxazole and benzothiazole derivatives
hydrochloride played a crucial role in amide activation followed nucleophilic attack that through eliminations of amine as a side product, and de-hydrolysis step leads to final annulation. This versatile strategy is applicable to a wide variety of differently substituted o-aminophenols, unactivated aliphatic and aromatic amides, yielding the corresponding product in good to excellent yields in a single step