New asymmetric transformation of optically active allene-1,3-dicarboxylate and its application to the formal asymmetric synthesis of (–)-epibatidine

Abstract

A new efficient synthesis of di-(–)-L-menthyl (R)-allene-1,3-dicarboxylate [(R)-1] involving asymmetric transformation through epimerization–crystallization with the assistance of a catalytic amount of Et₃N was developed; the highly endo-selective asymmetric Diels–Alder reaction of (R)-1 with N-Boc-pyrrole for the asymmetric synthesis of 7-tert-butoxycarbonyl-7-azabicyclo[2.2.1]heptan-2-one [(–)-6], a synthetic intermediate of (–)-epibatidine, is described.