Synthesis of ent-gabosine E from d-mannose by intramolecular nitrone–olefin cycloaddition

Intramolecular nitrone–olefin cycloaddition in a mannose template followed by N–O cleavage, quaternization of the resulting amine, and finally oxidative elimination of the amino group affords, after deprotection, ent-gabosine E in enantiomerically pure form.