Diversity-oriented synthesis of benzo[b]thiophenes fused to medium-sized N-heterocycles via Friedel–Crafts cyclization processes

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.S COCH 3 -Expedient synthesis -High regioselectivity -Wide starting scope -Mild reaction condition Simple reaction steps S N Ar n CO 2 Et a-f Ar = Ph or 2-Pyridyl n = 0 or 1 or 2 Friedel-Crafts cycliacylations a: n = 0, Y = CH; b: n = 1, Y = CH;