methyl (1R,3S,5R,6R)-3-methyl-6-hydroxybicyclo<3.2.0>heptane-3-carboxylate

methyl (1R,3S,5R)-3-methyl-6-oxobicyclo<3.2.0>heptane-3-carboxylate

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