methyl (2S,3aR,6aS)-1,2,3,3a,4,5,6,6a-octahydro-2-methyl-4-oxopentalene-2-carboxylate

(2S,3aR,3bS,7aS)-2,3,3a,3b,4,5,7,7a-octahydro-2,3b-dimethyl-5-oxo-1H-cyclopentapentalene-2-carboxylic acid

(2S,3aR,3bR,6aS,7aS)-4,4-Dichloro-2,3b-dimethyl-5-oxo-decahydro-cyclopenta[a]pentalene-2-carboxylic acid methyl ester

methyl (2S,3aR,3bR,6aS,7aS)-2,3,3a,3b,4,5,6,6a,7,7a-decahydro-2,3b-dimethyl-5-oxo-1H-cyclopentapentalene-2-carboxylate

methyl (2S,3aR,3bS,7aS)-2,3,3a,3b,4,5,7,7a-octahydro-2,3b-dimethyl-5-oxo-1H-cyclopentapentalene-2-carboxylate