Hypervalent iodine-mediated synthesis of benzoxazoles and benzimidazoles via an oxidative rearrangement

Abstract

A Beckmann-type rearrangement of o-hydroxy and o-aminoaryl N–H ketimines has been developed to prepare benzoxazoles and N-Ts benzimidazoles, respectively. The ketimine derivatives were easily prepared by condensation of ammonia with the corresponding ketones and (diacetoxyiodo)benzene was found to act as an efficient oxidant to trigger the [1,2]-aryl migration towards the formation of the desired heterocycles. Depending on the substitution pattern, the results revealed another mechanistic pathway through which benzisoxazoles or 1H-indazoles could be formed. The Beckmann-type rearrangement strategy was applied to the synthesis of benzimidazole-containing biorelevant targets such as chlormidazole and clemizole.