Formylation of iron(III) porphyrins and chlorins of natural origin

Abstract

Iron(III) porphyrins and chlorins are convenient starting materials for the preparation of labile formylated derivatives by the Vilsmeier procedure. Porphyrins and chlorins bearing vinyl substituents yield 3-oxoprop-1-enyl derivatives. Both cis- and trans-isomers are formed, the latter predominating. Relative reactivities appear to be vinyl > meso-proton > β-proton. The n.m.r. and visible spectra of the products of formylation of deuteroporphyrin IX, mesoporphyrin IX, protoporphyrin IX, chlorin-e₆ and isochlorin-e₄methyl esters are compared with the spectra of other formylporphyrins and chlorins.