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

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

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

(3aS,5S,6aR)-5-Methyl-1-oxo-octahydro-pentalene-2,5-dicarboxylic acid 2-ethyl ester 5-methyl ester

methyl (2aR,2bR,4S,5aS,6aS)-decahydro-2,2-dichloro-2a,4-dimethyl-1-oxocyclobutapentalene-4-carboxylate