2,6-diphenyl-3a,4,8,8a-tetrahydropyrrolo[3,4-f]isoindole-1,3,5,7(2H,6H)-tetraone

5-phenyl-1,3-dihydro-thieno[3,4-c]pyrrole-4,6-dione

5-phenyl-1,3-dihydro-4H-thieno[3,4-c]pyrrole-4,6(5H)-dione 2,2-dioxide

2,2,4,4-tetrahydrothiophene-3,4-dicarboxylic acid anhydride

dimethyl 2,5-dihydrothiophene-3,4-dicarboxylate