Syntheses and properties of benzodipyrrinones

2,3‐Benzannelated dipyrrinone analogs ( 1 and 2 ) of xanthobilirubic acid ( 3 ) are prepared by base‐catalyzed condensation of isoindolinone ( 5 ) and indolin‐2‐one ( 6 ) respectively, with methyl 3‐(2‐formyl‐3,5‐dimethyl‐1H‐pyrrol‐4‐yl)propanoate ( 4 ). Nuclear Overhauser effect H‐nmr studies indicate that both 1 and 2 adopt preferentially a syn‐Z configuration. The former forms a hydrogen‐bonded homodimer in nonpolar solvents; the latter is intramolecularly hydrogen bonded.