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

摘要

Substituted azafulvenes were generated by dehydrogenation of 5′-methyl-substituted pyrromethenones withDDQand 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 ofDDQon a 5′-methylpyrromethenone and was quenched by an 5′-unsubstituted pyrromethenone. The resulting rubinoid adduct was dehydrogenated immediatly byDDQ— yields were good