A Simple and Efficient Synthesis of fused Benzo[b]thiophene Derivatives

A new approach to the synthesis of fused benzothiophene derivatives was developed based on iodine-promoted photo-cyclization of 4,5-diarylsubstituted thiophenes obtained in three steps from commercially available compounds. Comparative analysis showed that photochemical cyclization is a more efficient method for the preparation of fused benzo[b]thiophene derivatives, compared to oxidative coupling 4,5-diarylsubstituted thiophenes in the presence of iron (III) chloride and palladium catalyzed intramolecular arylation. This approach provides an efficient synthesis of functionally substituted naphtho[2,1-b: 3,4-b ']dithiophenes, phenanthro[9,10-b] thiophenes, benzo[1,2-b: 3,4-b': 6 , 5-b '']trithiophenes, as well as new fused heterocycles containing a pyridine ring and / or a carbazole moiety