Formation of 2H‐thiopyrans and thiophenes by thermal rearrangement of propargyl vinyl sulfide or its homologues and 2‐alkynyl thienyl sulfides

Abstract
2H‐Thiopyran and a number of derivatives have been obtained in fair to good yields by heating compounds containing the system C ≡ CCSCC, in hexamethylphosphorictriamide. Mixtures of 2H‐thiopyrans and thiophenes are formed when heating is performed in this solvent or in dimethyl sulfoxide in the presence of amines. Thiopyrans, having an alkyl group on ring carbon atom 4, are partly converted into the “exo”‐compounds 4‐alkylidene‐2,3‐dihydro‐4H‐thiopyrans.