Polysubstituted Oxygen Heterocycles by a Reformatsky-Type Reaction/Reductive Cyclization Approach from Enantiopure β-Ketosulfoxides

The stereoselective synthesis of tetrasubstituted tetrahydrofurans and trisubstituted tetrahydropyrans bearing a sulfoxide was achieved by reductive cyclization (Et₃SiH/TMSOTf) from the corresponding enantiopure hydroxy ketones protected as a dioxolane. These derivatives are easily accessible from a Reformatsky-type reaction between α-bromo-α‘-sulfinyl ketones and protected α- or β-ketoaldehydes, followed by diastereoselective reduction of the resulting β-ketosulfoxide.