(2R,3aS,3bS,7aS)-6a-Hydroxy-2,3b-dimethyl-4-methylene-5-oxo-decahydro-cyclopenta[a]pentalene-2-carboxylic acid methyl ester

4α-(3-oxo-1-buten-2-yl)-7α-carbomethoxy-4β,7β-dimethyl-(1α,5α)-bicyclo<3.3.0>octan-3-one