Protecting-Group-Free Formal Synthesis of Aspidospermidine: Ring-Opening Cyclization of Spirocyclopropane with Amine Followed by Regioselective Alkylations

A concise formal synthesis of (+/-)-aspidospermidine via Stork's intermediate, which could be used as a divergent synthesis of Aspidosperma alkaloids, was achieved by employing a ring-opening cyclization of spirocyclopropane with amine followed by a regioselective intramolecular/intermolecular alkylation sequence. Stork's intermediate was synthesized in only six steps from a simple starting material, 1,3-cyclohexanedione, and was converted into (+/-)-aspidospermidine. To the best of our knowledge, this synthesis of Stork's intermediate involves the least number of steps to date. Furthermore, no protecting groups were used during this synthesis.