Asymmetric Synthesis of Uncinatone, Bracteatum A, Trichotomone F, and Caryopterisoid C

We report the collective total syntheses of four 17(15→16),18(4→3)-diabeo-abietane diterpenoids via a concise and enantioselective route (11-13 steps). Central to this strategy is a bioinspired polyene cyclization/Wagner-Meerwein rearrangement cascade, which directly forges the challenging tricyclic framework with high enantioselectivity. A subsequent Pd-catalyzed intramolecular cross-electrophile coupling efficiently assembles the key 6/6/6/5 tetracyclic core. This core serves as a versatile platform for accessing these diterpenes and can be elaborated into caryopterisoid C (6), a compound with anti-AKI activity. Furthermore, we demonstrate for the first time that ceric ammonium nitrate can mediate an epoxidation reaction.