[1R,6R,(+)]-1α-[[(1S,4aR)-Decahydro-6β-hydroxy-5,5,8aβ-trimethyl-2-methylenenaphthalene-1β-yl]methyl]-5β-hydroxy-4-(hydroxymethyl)-7-oxabicyclo[4.1.0]hepta-3-ene-2-one