Efficient Synthetic Access to the Hetisine C20-Diterpenoid Alkaloids. A Concise Synthesis of Nominine via Oxidoisoquinolinium-1,3-Dipolar and Dienamine-Diels−Alder Cycloadditions

Abstract

A concise synthetic approach to the hetisine C₂₀-diterpenoid alkaloids is reported. The total synthesis of (±)-nominine was accomplished in a 15-step sequence employing a dual cycloaddition strategy. Key features of the synthesis include a reversible intramolecular 4-oxidoisoquinolinium betaine dipolar cycloaddition in conjunction with a pyrrolidine-induced dienamine isomerization/Diels−Alder cascade.