Synthesis of small‐medium ring thioanhydrides

Abstract Reaction of five‐membered ring anhydrides with sodium sulfide has previously been employed for synthesis of the corresponding thioanhydrides in low yields. Re‐examination of the stoichiometry reveals reaction of cyclic anhydride with sodium sulfide (2:1 respectively), affords the thioanhydride accompanied by the corresponding dicarboxylate in a 1:1 molar ratio. The mechanistic pathway for this reaction has also been elucidated. Optimization of reaction conditions has resulted in the synthesis of a variety of four to seven‐membered ring thioanhydrides in yields approaching theoretical.