Reactivity of pyrrole pigments, III. Fragmentation of nitro derivatives of pyrrole pigments and its relationship to the Gmelin reaction

Abstract

Abstract The 5‐(arylnitromethylene)‐3‐pyrrolin‐2‐ones 1‐5 , the 5‐nitrobilin‐ 1,19 ‐diones 7,8 , and the 5‐nitropyrromethenone 6 are shown to decompose in acidic media to yield maleimides according to fragmentation reactions of nitronic acids. This fragmentation reaction elucidates the nature of the Gmelin reaction and the formation of the “Nitritkörper” (methylvinylmaleimide) by nitrous acid treatment of bilirubin.