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

Abstract

An enantioselective approach toward the synthesis of the spiroalkaloid (-)-nitramine was achieved by electrophile-induced cyclization of a suitably substituted and protected chiral α-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.