Beiträge zur Chemie der Pyrrolpigmente, 40. Mitt.: Azafulvene,Schlüsselstellen beim Aufbau von Pyrrolpigmenten? —Eine neue Synthese von verdinoiden und rubinoiden Gallenfarbstoffen

Substituted azafulvenes were generated by dehydrogenation of 5-methyl-substituted pyrromethenones withDDQ and characterized by UV- and¹H-NMR-spectroscopy. Their electrophilic properties were demonstrated using several quenchers and furthermore they were used for a synthesis of verdinoid bile pigments (which easily can be converted to rubinoid systems by the action of NaBH₄) with nearly any desired unsymmetrical alkyl substitution patter: The azafulvene spezies was generated by the action ofDDQ on a 5-methylpyrromethenone and was quenched by an 5-unsubstituted pyrromethenone. The resulting rubinoid adduct was dehydrogenated immediatly byDDQ — yields were good to high.

39. Mitt.:Falk, H., Höllbacher, G., Hofer, O., Müller, N., Mh. Chem.112, 391 (1981).