General Synthesis of Hydrocarbon-Soluble Porphyrins

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1.3, 5, 7-Tetramethyl -2, 4, 6, 8-tetra(n-pentylIporphvrin (2) and 2, 4.6, 8-tetrain-heptyl)-1, 3.5.7-tetramethvlporphyrin (3) were synthesized in good yield by a general route from benzyl 3-formyl-2.4-dimethvlpyrrole-5-carboxylate (4); the final porphyrin cyclization was brought about by self-condensation of the appropriate pyrromethene salt in hot formic acid. Porphyrins 2 and 3 were shown to be approximately 14 times more soluble in toluene than is etioporphyrin I [2, 4, 6, 8-tetraethyl-l, 3.5.7-tetramethylporphyrin (20)] and to have considerably lower melting points 2, 199C: 3, 124 C; 20, 300 C], Activation of the porphyrins 2 and 3 for future attachment of thiolate and imidazole-bearing substituents at the meso (methine) positions was carried out by Vilsmeier formylation[of the copper(II) complex], reduction with sodium borohvdride. and then treatment of the resulting hydroxymethylporphyrins with acetic anhydride in pyridine to give the electrophilic aeetoxymethylporphyrin derivatives. © 1979, American Chemical Society. All rights reserved.

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Journal of Organic Chemistry

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