Syntheses of methyl-devinylporphyrins related to protoporphyrin-IX. Initial studies on the mechanism of the copper (II) catalysed cyclization of 1′,8′-dimethyl-a,c-biladiene salts
Using copper (II) catalysed cyclization of a,c-biladiene dihydrobromide salts, porphyrins [(3)–(5)] related to protoporphyrin-IX dimethyl ester (8), but in which both vinyls are replaced with methyls, or where either the 2- or 4-vinyls are individually replaced with methyls, are synthesized. These compounds are required for reconstitution of the corresponding hemes into hemoproteins, to enable the study of the rotational disorder of prosthetic heme groups in reconstituted hemoproteins. By way of 13C n.m.r. spectroscopy of enriched a,c-biladienes and porphyrins, the copper(II) catalysed cyclization of 1′,8′-dimethyl-a,c-biladiene dihydrobromides is shown to afford porphyrins in which one of the 1′- and 8′-methyl groups becomes the new linking meso carbon atom.