Radical-Cascade Avenue for 3,4-Fused-Ring-Substituted Thiophenes.

A single-step intramolecular radical cascade reaction of diynes and thioacetic acid in the presence of a catalytic amount of azobis(isobutyronitrile) as a radical initiator has been developed to synthesize thiophenes. This method allows easy and effective construction of a thiophene scaffold having 3,4-fused-ring substitution and unsubstituted 2,5-positions for further functionalization and polymerization. Using this method, derivatives of cyclopenta[ c]thiophene, 3,4-ethylenedioxythiophene, and thiophene-containing spirocyclic compound have been synthesized.