EFFICIENT ONE-POT SYNTHESIS OF BENZOXAZOLE DERIVATIVES CATALYZED BY NICKEL SUPPORTED SILICA

Abstract

A simple and efficient method has been developed for the synthesis of benzoxazoles from 2-aminophenol and substituted aldehydes in the presence of a catalytic amount of nickel supported silica at room temperature. . Two protocols for the synthesis of benzoxazoles have been developed. One is the copper-catalyzed intramolecular o-arylations or intermolecular domino annulations of o-arylhalides 2-4 and the other is the direct condensation of 2-aminophenol with carboxylic acid or aldehyde under harsh conditions, such as in the presence of strong acid, high temperature 5 or strong oxidants 6-9 . Catalytic aerobic oxidation using oxygen as terminal oxidant has received much attention 10,11 and been used in the synthesis of benzoxazoles 12,13 . Nickel supported silica as an environmental friendly and economical catalyst has been attracting increasing research interest from chemists 14 . Although kinds of Ni supported SiO2 catalyzed organic transformations have been developed, the Ni-SiO2 to form carbon-carbon and carbon-heteroatom bond has remained largely undeveloped 15 . Herein, we report an efficient and environmentally friendly method for the synthesis of benzoxazoles catalyzed by nickel supported silica at room temperature (Scheme 1). We studied the possibility to synthesis of benzoxazoles by the reaction of 2-aminophenol and substituted aldehyde using Ni-SiO2 as the catalyst (Scheme 1). Here, an efficient and simple method for the synthesis of target compounds is described and the synthesis of some compounds has been reported in our previous studies.