Hydride-Promoted Ring Expansion of 2-Azaspiropyrrolinium Salts: An Approach Towards the Synthesis of (-)Nitramine

An enantioselective approach toward the synthesis of the spiroalkaloid (-)-nitramine was achieved by electrophile-induced cyclization of a suitably substituted and protected chiral (alpha)-allylcyclohexanecarboxaldimine. Its hydride-promoted ring expansion after spirocyclization gave rise to the competitive formation of isomeric spiropyrrolidines and a spiropiperidine, the latter being further transformed into (-)-nitramine.