3-[(1R,4aR,5S,6S,8aS)-6-(tert-butyldimethylsiloxy)-5,8a-dimethyl-2-methylene-5-(4-methylpent-3-enyl)-decahydronaphthalen-1-yl]hydroxymethyl-5,6-dimethyl-2-methoxy-4H-pyran-4-one