Phosphine-Catalyzed Enantioselective [4 + 2] Annulation of o-Quinone Methides with Allene Ketones.

A phosphine-catalyzed highly enantioselective [4 + 2] annulation between ortho-quinone methides and allene ketones has been developed. The reported method led to the formation of chromane derivatives in high yields and excellent enantioselectivity. This is the first time that ortho-quinone methides are employed in phosphine-mediated cyclization reactions.