Enantioselective Total Syntheses of Grayanane Diterpenoids and (+)-Kalmanol: Evolution of the Bridgehead Carbocation-Based Cyclization and Late-Stage Functional Group Manipulation Strategies.

Grayanane diterpenoids contain over 300 highly oxidized and structurally complex members, many of which possess important biological activities. Full details are provided for the development of the concise, enantioselective and divergent total syntheses of grayanane diterpenoids and (+)-kalmanol. The unique 7--trig cyclization based on a bridgehead carbocation was designed and implemented to construct the 5/7/6/5 tetracyclic skeleton, demonstrating the practical value of the bridgehead carbocation-based cyclization strategy.

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--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.