New chemistry of oxophlorins (oxyporphyrins) and their pi-radicals

Syntheses of novel 15-substituted-oxophlorins via the MacDonald condensatio n of diformyl-dipyrroketones and 5-substituted-dipyrromethanes are describe d. The electronic and steric features of the 15-substituent enable facile c ontrol over the oxidation potential of the oxophlorins. Introduction of an electron-withdrawing group efficiently minimizes the formation of oxophlori n pi-radicals. Stabilization of neutral pi radicals is promoted by hypercon jugation 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 compl exation to divalent metals. Radical formation, enhanced by mild oxidants su ch as K3FeCN6, yielded pure oligomers and stereospecific supramolecular arr ays by radical dimerizations taking place at the 10- and 10'-positions, (C) 1999 Elsevier Science Ltd. All rights reserved.