Synthesis of benzo[2,1-b:3,4-b']dithiophene-4,5-dione derivatives

The 1-trimethylsilylimidazole-mediated thiophene ring formation from 6-acylbenzo[b]thiophene-4,5-diones (3), which were prepared utilizing photoacylation of benzo[b]thiophene-4,5-dione (1) with aliphatic aldehydes, and ethyl mercaptoacetate, followed by acid hydrolysis and oxidation with cerium(IV) ammonium nitrate (CAN), led to one-pot formation of the 3-substituted ethyl 4,5-dioxo-4,5-dihydrobenzo[2,1-b:3,4-b'jdithiophene-2-carboxylates (4) in satisfactory yields.