Synthesis studies directed toward gelsemine. Preparation of an advanced pentacyclic intermediate

Abstract Pentacyclic gelsemine intermediate 2 was prepared from 3 by a six step sequence whose key steps are (a) intramolecular Mannich cyclization of an N-acyliminium ion intermediate to form the azatricyclo [4.4.0.0 2,8 ] decane ring system, and (b) palladium catalyzed intramolecular alkene arylation to elaborate the spirooxindole.