Synthesis of the Pentacyclic Framework of the Alkaloid Tronocarpine

A short and efficient synthesis of the pentacyclic core of the indole alkaloid tronocarpine is described. The synthetic pathway involves several easily accomplished steps, including a radical oxidative aromatic substitution reaction on the N-tert-butoxycarbonyl-protected tryptamine and a xanthate, a 1,4-1,2-nucleophilic addition between a 2,3-disubstituted indole and an ,-unsaturated aldehyde, and a Ti-mediated Dieckmann condensation. This report represents a significant advance in the quest for the first total synthesis of tronocarpine.