(1’R,3aS,4S,5aS,6R,8aS,8bS)-chloromethyl6-((ethoxycarbonyl)oxy)-4-hydroxy-2′,5a-dimethyl-4′-oxo-2,3a,4,5,5a,6,7,8,8a,8b-decahydro-1H-spiro[as-indacene-3,1′-cyclohexa[2,5]diene]-6-carboxylate