(3R,3′R,3aR,6S,7S,11aS,11bR)-6,7,11,11a-Tetrahydro-3a,7-dihydroxy-2′,2′,3,6,8,11a-hexamethyl-12-methylenespiro[3aH-6,11b-methano-3H-benzo[e]furo[3,4-c]oxocin-9(10H),3′(6′H)-[2H]pyran]-1,4,6′-trione