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■ Efficient and Divergent Synthesis of Benzoxazoles and 1,2-Benzisoxazoles from o-Hydroxyaryl Ketoximes

Zhenhua Li,* Guoqiang Jin, Jingjing Qin, Zhiyong Tan, and Jiayu He

*College of Pharmaceutical Sciences, Zhejiang University of Technology, No.18 Chaowang Road, 6th Zhaohui District, Hangzhou, Zhejiang Province 310014, China

Abstract

A bis(trichloromethyl) carbonate (BTC) / triphenylphosphine oxide (TPPO) system promoting tunable cyclization of a variety of o-hydroxyaryl ketoximes to benzoxazoles and benzisoxazoles was developed. The synthetic switch was enabled by base-free or the use of Et3N. Under base-free conditions, o-hydroxyaryl ketoximes were treated with BTC/TPPO giving corresponding 2-substituted benzoxazoles via cascaded Beckmann rearrangement and intramolecular oxa-cyclization. Analogously, the 3-substituted benzisoxazoles were obtained via intramolecular nucleophilic substitution reactions in the presence of Et3N. This process features mild reaction conditions, high chemoselectivity, and good functional groups tolerance.