Asymmetric synthesis of enantiomerically pure 7-isopropenyl-4a-methyl-3-methyleneoctahydrochromen-2-ones

Four stereoisomers of 7-isopropenyl-4a-methyl-3-methyleneoctahydrochromenon-2-one have been obtained for the first time. The key step of the synthesis involves asymmetric Michael addition of chiral enamines derived from dihydrocarvone to acrylate 1. Absolute configurations were established by X-ray analysis.