Unprecedented convergent synthesis of the fused tricyclic thiophenes via Friedel-Crafts cycliacylation reactions

An efficient and concise procedure toward benzo-and pyridothieno[2,3-b] fused N-heterocycles from readily available substrates is described. The process involves Lewis and Bronsted acids-mediated Friedel-Crafts cyclizations of the synthesized thiophene-based carboxylic acid precursors into new tricyclic thiophenes. The method efficiently achieves the promising pharmaceutically polycyclic thiophenes in good yields. [GRAPHICS] .