(3bS,4aS,5aS,6aS,7aS,7bS,8aS,8bS)-3b,4,4a,7a,7b,8b,9,10-Octahydro-8b-methyl-6a-(1-methylethyl)-trisoxireno[4b,5:6,7:8a,9]phenanthro[1,2-c]furan-1,6(3H,6aH)-dione