Hafnium(IV)-Salen-Catalyzed Highly Reactive and Enantioselective Epoxidation Directed by Amides

Substrate-directed enantioselective olefin epoxidation was limited to a few types of directing groups and relatively low catalyst activities. Herein, an expeditious asymmetric epoxidation protocol is reported for allylic amides and sulfonamides using a hafnium-BINAM-salen catalyst with high enantioselectivity and turnover frequency. Aryl carboxamides of allylic amines with a trisubstituted olefin motif were suitable substrates. Sequential intramolecular ring-opening in a one-pot reactor furnished highly enantiopure oxazoline alcohols. Crystallographic studies suggested the catalyst possessed a mononuclear cis-alpha configuration. Computational studies of the transition state indicated that this conversion underwent a substrate-directed pathway.