1,3-dicyano-2,2-dimethyl-cyclobutane-1,3-dicarboxylic acid
1,3-dicarbamoyl-2,2-dimethyl-cyclobutane-1,3-dicarboxylic acid
6,6-dimethyl-2,4-dioxo-3-aza-norpinane-1,5-dicarbonitrile
2,2-dimethylcyclobutane-1,1,3,3-tetracarboxylic acid
cis-3-carboxy-2,2-dimethylcyclobutylmethanoic acid