Regioselective synthesis of pyrrolo[1,2-a]imidazoles and imidazo[1,2-a]-pyridines

A concise and efficient synthesis of pyrrolo[1,2-a]imidazoles and imidazo[1,2-a]-pyridines was developed by regioselective aza-ene additions and regioselective cyclic–condensation reactions of heterocyclic ketene aminals with ethyl 3-benzoylacrylate or methyl acetylacrylate derivatives under catalyst-free conditions. This method has some advantages including high regioselectivity, good yields and simple work-up procedures.