Unified Total Synthesis of Benzenoid and Troponoid Diterpenoids Enabled by Regiocontrolled Phenol-to-Tropone Ring Expansion.

Herein, we present a unified strategy for the total synthesis of benzenoid and troponoid diterpenoids, specifically cephanolides A and B (benzenoids) and harringtonolide and cephinoid H (troponoids), in 13 to 19 longest linear steps. This synthesis relies on a palladium-catalyzed Csp-Csp cross-coupling followed by an intramolecular doubly electron-deficient Diels-Alder reaction to establish the core skeleton and complete the synthesis of the benzenoids. A late-stage regioselective phenol-to-tropone ring expansion was developed to convert the benzenoids to the corresponding troponoid congeners. This work provides a regiocontrolled approach for achieving the synthetic connectivity between benzenoid and troponoid diterpenoids.