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.