Enantioselective Synthesis of Dihydrothiopyranones via NHC-Catalyzed [3 + 3] Annulation of 2-Bromoenals with β-Oxodithioesters.

The N-heterocyclic carbene (NHC)-organocatalyzed [3 + 3] annulation of 2-bromoenals with β-oxodithioesters resulting in the enantioselective synthesis of dihydrothiopyranones is presented. The chiral α,β-unsaturated acylazoliums generated from 2-bromoenals and carbenes underwent smooth interception with the sulfur nucleophiles to furnish the sulfur heterocycles in satisfactory yields/selectivity. The regioselective formation of dihydrothiopyranones over the competing dihydropyranones is noteworthy.