Tricyclo[3.2.2.02,4]non-8-ene-6,7-dicarboxylic anhydride

4,6-etheno-1H-cyclopropa[4,5]benzo[1,2-c]furan-1,3(4H)-dio

hexahydro-1H-4,6-ethenocyclopropa[4,5]benzo[1,2-c]furan-1,3(3aH)-dione

4,4a,5,5a,6,6a-Hexahydro-4,6-etheno-1H-cycloprop[f]isobenzofuran-1,3(3aH)-dione