(1aR)-1aβ,2,2a,4aβ,4bβ,6,9b,9cβ-Octahydro-2α-hydroxy-2aβ,9bα-dimethyl-3H,8H-furo[2,3,4:4,5]oxireno[7,8]naphtho[2,1-c]pyran-3,8-dione