Simple approach to optically active drimane sesquiterpenes based on enzymatic resolution

When the beta-acyloxy esters (+/-)-10 and (+/-)-11 were exposed to the lipase OF-360 from Candida rugosa or immobilized lipase OF-360 in a water-saturated organic solvent, the hydrolyzed product (8aS)-6 was obtained in high chemical (40%) and optical (> 99% ee) yields. The absolute structure of (8aS)-6 was confirmed by the fact that (8aS)-6 was converted into an authentic sample gamma-keto nitrile (8aS)-17. Treatment of the diol (+/-)-12 with isopropenyl acetate in the presence of the lipase Godo E-4 from Pseudomonas sp. provided the unchanged (8aR)-12 (89% ee) in 42% yield.