Construction of AE ring system for the C19-diterpenoid alkaloids with a 5β-hydroxyl group

An AE azabicyclic fragment, with a β-hydroxyl group at C-5 and a substituent at C-1, of the C19-diterpenoid alkaloids, was synthesized. The key reactions include an intramolecular Claisen-type condensation, double Mannich reaction, and stereoselective nucleophilic addition of carbonyl group with the assistance of steric effect of 1β-substituent.