Electrophilic substitution reactions of derivatives of deuteroporphyrin-IX: Deuteriation and Vilsmeier formylation

Treatment of protoporphyrin-IX, deuteroporphyrin-IX, 2,4- diacetyldeuteroporphyrin-IX, and mesoporphyrin-IX dimethyl esters [(3)-(6), respectively] with deuteriated toluene-p-sulphonic acid in hot o-dichlorobenzene accomplishes electrophilic deuteriation of the meso-protons at a rate which is dependent upon the nature of the 2- and 4-substituents in the porphyrin substrate. The vinyls, 2 and 4 hydrogens, and acetyls in (3), (4), and (5), respectively, are also exchanged under these conditions. A simple theory is put forward to explain the uneven amounts of meso-deuteriation, and the deuteriation at both the methylene and methine positions in the protoporphyrin-IX vinyl groups. Vilsmeier formylation of copper(II) deuteroporphyrin-IX dimethyl ester (10) using N,N-di-isobutylformamide in place of dimethylformamide yields products arising predominantly from 2- or 4-formylation of the substrate; a small quantity of α or β meso-formylporphyrin is also obtained