Syntheses of novel 15-substituted-oxophlorins via the MacDonald condensation of diformyl-dipyrroketones 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 pi-radicals. Stabilization of neutral pi 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, (C) 1999 Elsevier Science Ltd. All rights reserved.
Khoury, R.g., Jaquinod, L., Paolesse, R., Smith, K.m. (1999). New chemistry of oxophlorins (oxyporphyrins) and their pi-radicals. TETRAHEDRON, 55(22), 6713-6732 [10.1016/S0040-4020(99)00319-1].
New chemistry of oxophlorins (oxyporphyrins) and their pi-radicals
PAOLESSE, ROBERTO;
1999-01-01
Abstract
Syntheses of novel 15-substituted-oxophlorins via the MacDonald condensation of diformyl-dipyrroketones 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 pi-radicals. Stabilization of neutral pi 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, (C) 1999 Elsevier Science Ltd. All rights reserved.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
