Studies on quinones. VII. Synthesis of some benzo[b]thiophene‐4,7‐diones

The synthesis of methyl 4,7‐dihydro‐4,7‐dioxobenzo[b]thiophene‐2‐carboxylate (20) based on the reaction of methyl mercaptoacetate with activated 1,4‐benzoquinones is described. Methyl 4,7‐dihydro‐4,7‐dioxo‐5‐hydroxybenzo[b]thiophene‐2‐carboxylate (24) and its corresponding methyl ether 26 were obtained through a Thiele‐Winter acetoxylation on 20. On the basis of the properties of methyl 4,7‐dihydro‐4,7‐dioxo‐6‐methoxy‐benzo[b]thiophene‐2‐carboxylate (21) obtained from 2,4,5‐trimethoxybenzaldehyde (32), the structures of the products 24 and 26 are proposed.