New entry to benzo[b]thieno[2,3-b]- and benzo[b]thieno-[3,2-b]-pyridines using 2- and 3-azidobenzo[b]thiophene as the nitrogen precursors

Abstract

N-(3-Benzo[b]thienyl)- and N-(2-benzo[b]thienyl)-imino-triphenylphosphorane—prepared from the corresponding azidobenzo[b]thiophenes—react with α,β-unsaturated aldehydes under mild conditions to give directly benzo-[b]thieno[3,2-b]- and benzo[b]thieno[2,3-b]-pyridines through electrocyclization (and eventual dehydrogenation) of the initial aza Wittig imine products.