Construction of Heteroacenes with Fused Thiophene and Pyrrole Rings via the Fischer Indolization Reaction.

A convenient approach to ladder-type 6H-benzo[4',5']thieno[2',3':4,5]thieno[3,2-b]indoles bearing various substituents in both terminal benzene rings has been developed. The protocol suggested for preparing these N,S-heteroacenes is based on using easily available reagents, such as cinnamic acids and arylhydrazines, which can be involved in the Fischer indole synthesis, as the key step. A similar condensed system of 12H-benzo[4″,5″]thieno[2″,3″:4',5']thieno[2',3':4,5]thieno[3,2-b]indole, bearing six rings, has also been obtained.