Pyrroles and related compounds. Part XIII. Porphyrin synthesis through b-oxobilanes and oxophlorins (oxyporphyrins)

Abstract

Condensation of 5′-benzyloxycarbonylpyrromethane-5-carboxamides with 5-benzyloxycarbonylpyrromethanes by means of phosphoryl chloride yeilds imine salts, which can be hydrolysed to well defined, crystalline b-oxobilanes. Hydrogenolysis of the two benzyloxycarbonyl groups in these compounds, followed by cyclisation with methyl orthoformate under acidic catalysis and aeration, yields oxophlorins. These oxophlorins are efficiently converted into porphyrins by acetylation, hydrogenation with elimination of acetic acid, and dehydrogenation. Three examples of this porphyrin synthesis are given, including coproporphyrin-III tetramethyl ester and mesoporphyrin-IX dimethyl ester, and its generality is discussed.