6-Oxopyriphlorins

Abstract

Reaction of 2,6-pyridinedicarbaldehyde with a series of tripyrranes in the presence of trifluoroacetic acid, followed by oxidation of a pyriphlorin intermediate with silver(I) acetate, gave 6-oxopyriphlorins in moderate to good yields. The oxophlorin analogues were nonaromatic porphyrinoids that gave bright green colored solutions. Protonation with TFA afforded species that were attributed to mono- and dicationic structures. The proton NMR spectra in TFA–CDCl₃ showed downfield shifts to the meso-protons and upfield shifts to the interior NH resonances that indicated the presence of a weakly diatropic dicationic species. Reaction of a 6-oxopyriphlorin with nickel(II) acetate in DMF or palladium(II) acetate in acetonitrile afforded the corresponding metallo-derivatives.