Enantioselective route to 3-vinylidene tetrahydropyrans and 3-vinylidene oxepanes based on a silyl-Prins cyclization

A general method has been developed for the asymmetric synthesis of 3-vinylidene tetrahydropyrans and 3-vinylidene oxepanes based on the Lewis acid-catalyzed intramolecular reactions of oxocarbenium ions with propargylsilanes. The observed excellent diastereoselectivity and a high asymmetric induction offer a new synthetic method with a wide scope and generality.