New chemistry of oxophlorins (oxyporphyrins) and their π-radicals
Syntheses of novel 15-substituted-oxophlorins via the MacDonald condensation of diformyldipyrroketones and 5-substituted-dipyrromethanes are described. The electronic and steric features of the 15-substituent enable facile control over the oxidation potential of the oxophlorins. Introduction of an electron-withdrawing group efficiently minimizes the formation of oxophlorin π-radicals. Stabilization of neutral π radicals is promoted by hyperconjugation with a 15-tert-butyl group. A sterically induced stabilization of a novel non-aromatic tautomer of oxophlorin, the so-called 'iso-oxophlorin' is demonstrated. These species exist also as 15-iso- oxophlorins upon complexation to divalent metals. Radical formation, enhanced by mild oxidants such as K3FeCN6, yielded pure oligomers and stereospecific supramolecular arrays by radical dimerizations taking place at the 10- and 10'-positions.
Publication Source (Journal or Book title)
Khoury, R., Jaquinod, L., Paolesse, R., & Smith, K. (1999). New chemistry of oxophlorins (oxyporphyrins) and their π-radicals. Tetrahedron, 55 (22), 6713-6732. https://doi.org/10.1016/S0040-4020(99)00319-1