The synthesis of four isomeric bisthienothiepinones

The displacement reaction between sodium thiophene-3-thiolate and methyl 3-(bromomethyl)thiophene-2-carboxylate (5) gave the expected thioether 7a. Basic hydrolysis afforded the carboxylic acid 7b; conversion to the acid chloride, and treatment of the latter with stannic chloride then produced the bisthienothiepinone 1. Using analogous reactions the isomers 2-4 were also synthesized.