Gallium(III)‐Catalyzed Cycloisomerization Approach to the Diterpenoid Alkaloids: Construction of the Core Structure for the Hetidines and Hetisines

A versatile core structure has been prepared that should provide a foundation for the syntheses of the hetidine- and hetisine-type diterpenoid alkaloids. The synthesis of the caged polycyclic core structure, which features nine contiguous stereocenters, utilizes a GaIII-catalyzed cycloisomerization of an alkynyl indene as well as a Michael/aldol sequence to build the bicyclo[2.2.2] framework.