Studies in sulphur heterocycles. Part 6. Convenient synthesis of 5-substituted benzo[b]thiophene derivatives and a facile entry to the thieno[2,3-g]indole system

Abstract

From 6,7-dihydrobenzo[b]thiophen-4(5H)-one and its 2-methyl derivative as starting materials 5-formyl, 5-acetyl, 5-carboxy, and 5-cyano-benzo[b]thiophene and 2-methylbenzo[b]thiophene, have been prepared in good to excellent yields. Benzo[b]thiophene-5-carbaldehyde on base catalysed condensation with ethyl azidoacetate, followed by thermal cyclisation of the resulting azidocinnamate provided a facile entry into the thieno[2,3-g] indole system.