Highly Efficient Synthesis of Tricyclic Amines by a Cyclization/Cycloaddition Cascade: Total Syntheses of Aspidospermine, Aspidospermidine, and Quebrachamine

Three in one: Three new rings can be made in one pot with complete control of the regio- and stereochemistry by a tandem cyclization/cycloaddition cascade reaction. Treatment of a chloroaldehyde with an amine gives a cyclic azomethine ylide that undergoes intramolecular cycloaddition onto a tethered alkene. The method was applied to the shortest known synthesis of aspidospermine (see scheme).