The cyanomethyl group for nitrogen protection and iminium ion generation in ring-enlarging pyrrolidine annulations. A short synthesis of the amaryllidaceae alkaloid d,1-crinine

The preparation of cis-3a-aryl-4-oxo-decahydrocyclohepta[b]pyrroles and cis-3a-aryl-4-oxo-octahydroindoles is facilitated by using a cyanomethyl group to both protect nitrogen and serve as a precursor for a formaldehyde iminium ion.