α , β-Unsaturated Carbonyls for One-Pot Transition-Metal-Free Access to 3,6-Dihydro-2 H -pyrans.

An efficient protocol has been developed for accessing mono-, di-, and trisubstituted 3,6-dihydro-2 H -pyran derivatives by simply subjecting α,β-unsaturated carbonyls to the carefully optimized Corey-Chaykovsky reaction conditions. The strategy provides selectively substituted dihydropyran derivatives in good to excellent yields with a broad substrate scope under very mild reaction conditions. Easy transformation of the final 3,6-dihydro-2 H -pyran to the valued 5,6-dihydro-2 H -pyran-2-one and tetrahydro-2 H -pyran derivatives expanded the scope of this methodology to diverse oxacycles. Further, the developed strategy also found application in a two-step route to racemic goniothalamin, which is widely studied for its cytotoxic behavior.