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 $\text{cis}$-3a-aryl-4-oxo-decahydrocycloheptab]pyrroles and $\text{cis}$-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.