Synthesis of benzo[1,2-b :5,4-b']dithiophene-4,8-dione derivatives

4,7-Dioxo-4,7-dihydrobenzo[b]thiophene-2-carboxylates (1) underwent regioselective acylation at the 5-position with a range of aldehydes under irradiation to give the corresponding 5-acyl-4,7-dihydroxybenzo[b]thiophene-2-carboxylates (2), which were then oxidized with Ag 2 O to afford 5-acyl-4,7-dioxo-4,7-dihydrobenzo[b]thiophene-2-carboxylates (3 ). These acylated benzothiophenquinone derivatives were transformed in one-pot to 4,8-dioxo-4,8-dihydrobenzo[1,2-b:5,4-b']dithiophene-2,6-dicarboxylates (5) by treatment with mercaptoacetates, followed by 1-trimethylsilylimidazole-mediated cyclization and cerium(IV) ammonium nitrate (CAN) oxidation.