Enantioselective Total Syntheses of Grayanane Diterpenoids: (−)-Grayanotoxin III, (+)-Principinol E, and (−)-Rhodomollein XX

Enantioselective total syntheses of (−)-grayanotoxin III, (+)-principinol E, and (−)-rhodomollein XX were accomplished based on a convergent strategy. The left- and right-wing fragments were assembled via the diastereoselective Mukaiyama aldol reaction catalyzed by a chiral hydrogen bond donor. The unique 7-endo-trig cyclization based on a bridgehead carbocation forged the 5/7/6/5 tetracyclic skeleton that underwent redox manipulations and 1,2-migration to access different grayanane diterpenoids.