(4aR,4bS,6aS,9aR,10aS,10bR)-6b-acetyl-4a,6a,8,8-tetramethyl-3,4,4a,4b,5,6,6a,6b,9a,10,10a,10b-dodecahydro-2H-naphtho[2',1':4,5]indeno[1,2-d][1,3]dioxol-2-one