Porphyrins. V. Studies on the cyclization of linear tetrapyrroles

Abstract

Condensation of 3-acetyl-2,4-dimethylpyrrole with the bis(methoxymethyl)-dipyrromethene (IV) has given the tetrapyrrene (I; R = Ac). This has been cyclized to 1,2-diacetyl-3,4,5,6,7,8-hexamethylporphin by heating with copper acetate in methanol. The yield was not as good as that reported for fully alkylated tetrapyrrenes, but the acetyl groups survived the reaction conditions. Similarly, condensation of 3-cyano-2,4-dimethylpyrrole with the bis(methoxymethyl)dipyrromethene (IV), gave the tetrapyrrene (I; R = CN). Cyclization under the same conditions gave two porphyrins, presumably 1-cyano-3,4,5,6,7,8-hexamethylporphin and 1,2-dicyano-3,4,5,6,7,8-hexamethylporphin, in poor yield.