An efficient access to benzo[b]thiophene-fused or -bridged to medium-sized N-heterocycles e.g. azocinones,
azoninones and azecinones, is described. The process involves cyclization of benzo[b]thiophene carboxylic
ester precursors, mediated by Lewis and Brønsted acids under suitable conditions. The ring closure precursors
were assembled starting from 2-acetylbenzo[b]thiophene. The developed strategy allows control of ring size
and offers easy access to fused benzo[b]thiophene polycycles of promising biological importance in moderate
to good yields.