Hypervalent iodine in the synthesis of bridgehead heterocycles: novel and facile syntheses of 3-substituted-5,6-dihydroimidazo[2,1-b]thiazoles and 3-phenylthiazolo[3,2-a]benzimidazole from acetophenones using [hydroxy(tosyloxy)iodo]benzene

Abstract

The synthesis of 3-substituted-5,6-dihydroimidazo[2,1-b]thiazoles 3a–f has been achieved by using a novel and facile method involving hypervalent iodine oxidation of acetophenones 1a–f with [hydroxy(tosyloxy)iodo]benzene, followed by the treatment of the resultant α-tosyloxyaceto-phenones 2a–f(generated in situ) with ethylenethiourea. The same approach starting from 1a and 2-mercaptobenzimidazole also supplied 3-phenylthiazolo[3,2-a]benzimidazole 7via the intermediate 2-phenacylmercaptobenzimidazole.