Use of a sterically demanding Lewis acid to direct ring expansion of monoactivated methylenecyclopropanes

A novel synthetic route for the preparation of functionalized alkylidene pyrrolidines via a MAD/n-Bu4NI-mediated ring expansion of monoactivated MCP was developed. The substrate scope for this reaction was found to be broad for a variety of aldimines and symmetrically as well as unsymmetrically monoactivated MCPs yielding the corresponding five-membered heterocyclic compounds in good yields (up to 92%). This methodology complements previous reports on the ring expansion of MCPs showing that selective syntheses of different heterocyclic scaffolds could be achieved from the same MCP by just changing the catalyst system.