Lanthanum(III) Triflate-Catalyzed Cyclopropanation via Intramolecular Methylene Transfer

A new method for cyclopropanation involving intramolecular methylene transfer from an epoxide to an olefin has been developed. This La(OTf)(3)-catalyzed process proceeds with good efficiency and with high stereoselectivity. A range of examples illustrating substrate scope are given along with a mechanistic rationale. Also demonstrated is an asymmetric cyclopropane synthesis that combines enantioselective epoxidation with this methylene-transfer protocol.