Polysubstituted oxygen heterocycles by a Reformatsky-type reaction/reductive cyclization approach from enantiopure beta-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 alpha-bromo-alpha'-sulfinyl ketones and protected alpha- or beta-ketoaldehydes, followed by diastereoselective reduction of the resulting beta-ketosulfoxide.