The porphyrinogen-porphyrin relationship: The discovery of artificial porphyrins

The oxidation of meso-tetrahydrotetraalkylporphyrinogen, which is the chemical and biochemical precursor of porphyrins, has been reexamined using meso-octaalkyl-porphyrinogen as a model compound. This investigation has led to the discovery of oxidized forms of porphyrinogen other than porphyrins, which we call artificial porphyrins. They contain cyclopropane moieties which function as two-electron shuttles via the formation and cleavage of a C-C bond. The metal-assisted modifications of the porphyrinogen skeleton, namely the homologation of a pyrrole to a pyridine ring using carbon monoxide and the functionalization of the aliphatic periphery, are the consequences of the bifunctional acid-base carrier properties of these metal-porphyrinogen complexes. This observation allowed us to establish general synthetic methodologies in the fields of metal-assisted C-H bond activation and C-C bond formation.