Enantiospecific Construction of Quaternary Carbon Center via Intramolecular 1,3-Dipolar Cycloaddition. A New Route to Natural (−)-Mesembrine from (S)-O-Benzylglycidol

Abstract
Thermolysis of the aziridine ester, obtained from (S)-O-benzylglycidol, afforded the pyrrolidine lactone bearing a quaternary carbon center stereo-specifically in a good yield via intramolecular cycloaddition of the 1,3-dipole. The adduct (11) could be converted into natural (−)-mesembrine, the major alkaloid of Sceletium namaquense, and its N-demethyl derivative via a 8 step sequence of reactions.