Synthesis of Alkylated Benzo[2,1-b:3,4-b′]dithiophenes by Annulative Coupling and Their Direct Arylation under Palladium Catalysis

The annulative coupling of 3,3′-diiodo-2,2′-bithiophene with internal alkynes efficiently proceeds in the presence of a palladium catalyst to afford the corresponding benzo[2,1-b:3,4-b′]dithiophene derivatives. The dithiophenes also undergo palladium-catalyzed direct arylation with aryl bromides at the 2- and 7-positions selectively.