A stepwise synthesis of unsymmetrical porphyrins

Abstract

1-Bromo-1,19-dideoxy-19-methyl(or ethyl)biladiene-ac dihydrobromides are prepared by condensation of the hydrobromide of a 5-bromo-5′-bromomethyldipyrromethene with that of a 5-unsubstituted 5′-methyl(or ethyl)-dipyrromethene in presence of stannic chloride. The 1,19-dideoxybiladiene-ac salts are cyclised to the corresponding porphyrins in good yield by maintaining a solution in o-dichlorobenzene at reflux temperature for 15 minutes. Several examples are described of the synthesis of porphyrins, including mesoporphyrin IX dimethyl ester, rhodoporphyrins I and XII diethyl esters, and γ-phylloporphyrins IV and XV methyl esters. An extension of the method using a 1,19-dibromo-1,19-dideoxybiladiene-ac dihydrobromide leads to syntheses of a monoazaporphyrin and a corrole, and the preparation of a diazaporophyrin is also described.