Synthetic entry to the hexacyclic Aspidosperma alkaloids. Total synthesis of (±)-4-hydroxyaspidofractinine

The pentacyclic intermediate (V) underwent a new type of Michael cyclization on the vinylogous amide system with acrylonitrile and methyl vinyl sulphone to give regio- and stereo-specific bridge formation producing the hexacyclic compounds which constitute the aspidofractinine (I) skeleton.