Total Synthesis of Terpenoids Employing a Benzannulation of Carvone Strategy: Synthesis of-()-Crotogoudin

Carvone is a sustainable and readily available starting material for organic synthesis. Herein, we present the syntheses of various natural product scaffolds that rely on a novel benzannulation involving the a-methyl group (C-10) of carvone to afford a versatile tetralin. The utility of our synthetic approach is highlighted by its application to a short synthesis of the ent-3,4-secoatisane diterpenoid (-)-crotogoudin. The 13-step enantiospecific synthesis features a regioselective double oxidative dearomatization, a Diels Alder cycloaddition with ethylene gas (to construct the bicydo[2.2.2] octane framework), and a final acid-mediated lactonization. The versatility of this benzannulation strategy is demonstrated by its utility in the preparation of the carbon skeleton of ent-3,4-seco-abietane diterpenoids using an intramolecular oxidative dearomatization.