Synthesis of 5‑Membered Sulfur Heterocycles via Tin-Catalyzed Annulation of Mercapto Ketones with Activated Alkenes

Efficient conversion of α-mercapto ketones 1 with activated alkenes 2 into S-heterocycles was developed with Sn­(Oct)2–2MeOH acting as a catalyst. Two types of products, dihydrothiophene 3 and thiolane 4, were obtained. The selectivity of the products was dependent on the reaction temperature and on the rearrangement of the S-heterocycles from 3 to 4 under heating conditions. The dihydrothiophenes 3 were transformed into useful thiolactones 6–8 and thiophene 9.