Synthetic study of yonarolide: stereoselective construction of the tricyclic core

Stereoselective construction of the tricyclic core of yonarolide (1), a marine norditerpenoid, was achieved. This synthetic route includes a Diels–Alder reaction and an intramolecular aldol condensation. It also involves efficient epimerization through a retro-Michael reaction–Michael addition and will be applicable to the total synthesis of 1.