Synthetic study of marine lobane diterpenes. Enantioselective syntheses oflobatrienolide and lobatrientriol from (+)-nopinone

The first enantioselective syntheses of highly oxygenated lobane diterpenes , (+)-lobatrienolide 4 and (+)-lobatrientriol 5, have been achieved, starti ng with (4R,5R)-1-acetoxy-4-isopropenyl-5-methyl-5-vinyl-cydohex-1-ene 10b which itself has been prepared from (+)-nopinone 7 as a versatile building block toward the asymmetric synthesis of natural products.