Benzazoles. Part 12. Synthesis of 2-(tetrahydro-2-thienyl)benzimidazoles and their unsaturated derivatives by the reaction of 2-mercaptoalkylbenzimidazoles with β-electrophilic ketones

Abstract

2-(α-Mercaptoalkyl)benzimidazoles (3) reacted with β-halogenoalkylketones (1) or with α,β-unsaturated ketones (2) to form the vinylogue adducts (4) which cyclised to give 2-(3-ydroxytetrahydro-2-thienyl)benzimidazoles (6). Compounds (4) or (6) reacted with acetic anhydride at room temperature to give the mono-(8) and diacetylated (9) derivatives of (6). At higher temperature dehydroacetylation occurs to give 2-(2,3-dihydro-2thienyl)benzimidazoles (11).