Synthesis of 3,4‐dihydro‐2h‐thiopyrans by the reaction of 4,5‐dihydrothiophenium‐1‐bis[ethoxy(and methoxy)carbonyl]methylides with sodium iodide

Sulfonium ylides 1a‐h reacted with sodium iodide to afford the corresponding thiopyrans 2a‐h. On the other hand, compounds 1a‐d were treated with thionyl chloride to give the ring opening products 3a‐d. The reaction of compounds 3a‐d with sodium iodide and triethylamine provided the corresponding thiopyrans 2a‐d.