Preparation of meso-unsubstituted porphyrins substituted with mono- and tetraformyl and other electron-withdrawing groups

A meso-unsubstituted porphyrin having a formyl group was synthesized both f rom a mono(ethoxycarbonyl)porphyrin by reduction with LiAlH4, followed by o xidation with MnO2 and from a monocyanoporphyrin by reduction with DIBALH. The monoethoxycarbonyl and monocyanoporphyrins were prepared by the acid ca talyzed mixed condensation of the corresponding 4-ethoxycarbonyl- and 4-cya no-2-(hydroxymethyl)pyrroles with 3-mesityl-4-methyl-2-(hydroxymethyl)pyrro le. A porphyrin with four formyl groups at the P-positions was prepared fro m ethyl 4-(dithiolan-2-yl)-3-methylpyrrole-2-carboxylate by the sequential treatment of LiAlH4, p-TsOH, and NBS. Cyclic voltammetry and UV-VIS spectro scopic analyses of these porphyrins revealed the highly electron-deficient property of the porphyrin chromophore.