(4R,4aR,6aS,7S,11aS,11bR)-4-hydroxy-3,4,4a,7,11a-pentamethyl-4a,5,6,6a,7,8,10,11,11a,11b-decahydro-1H-cyclohepta[a]naphthalen-9(4H)-one ethylene acetal