(1S,2S,5R)-1aβ,2,3,4,4aβ,5,6,7,7aβ,7bβ-Decahydro-2,4,4,6,6,7aβ-hexamethoxy-7bβ,8-di(2-propenyl)-1,2,5-metheno-1H-cyclobuta[de]naphthalene-3α,7β-diol