(1R,4aR,4bR,7S,9aS,10S,10aR)-Methoxymethyl 7-hydroxy-1-methyl-8-methylene-13-oxo-1,4,4b,5,6,7,8,9,10,10a-decahydro-4a,1-(epoxymethano)-7,9a-methanobenzo[a]azulene-10-carboxylate