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

tert-butyl cyclopent-3-ene-1-carboxylate

(1S,3S,5R)-6-Chloro-3,6-dimethyl-7-oxo-bicyclo[3.2.0]heptane-3-carboxylic acid

(2S,3aR,6aR)-4-Chloro-2,4-dimethyl-5-oxo-octahydro-pentalene-2-carboxylic acid methyl ester

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