4,8-Ethenopyrrolo[3',4':3,4]cyclobut[1,2-f]isoindole-2,6-dicarboxylic acid 1,3,3a,3b,4,4a,5,7,7a,8,8a,8b-dodecahydro-1,3,5,7-tetraoxo-, diethyl ester 4,8-Ethenopyrrolo[3',4':3,4]cyclobut[1,2-f]isoindole-2,6-dicarboxylic acid, 1,3,3a,3b,4,4a,5,7,7a,8,8a,8b-dodecahydro-1,3,5,7-tetraoxo-, diethyl ester NSC367334