dimethyl (3aS,7aS)-1,3,3a,7a-tetrahydro-2H-cyclopenta[a]pentalene-2,2-dicarboxylate

dimethyl 2-(2-(cyclopenta-2,4-dienylidene)ethyl)-2(3-oxopropyl)malonate

dimethyl (3aS,7aS)-3a-methyl-1,3,3a,7a-tetrahydro-2H-cyclopenta[a]pentalene-2,2-dicarboxylate