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.