Synthesis of rhodoporphyrin XV diethyl ester and related porphins

Abstract

The synthesis of porphins by cyclisation of the dihydrobromides of 1-bromo-19-methyl-1,19-dideoxybiladienes-ac in boiling o-dichlorobenzene has been extended to the preparation of certain rhodoporphyrins and related compounds. Dimethyl sulphoxide–pyridine can be used as an alternative solvent and the cyclisation then proceeds at room temperature. The effect on the yield of porphin of the proximity of the nuclear ester group to the point of cyclisation has been determined and the results have been used in a synthesis of rhodoporphyrin XV diethyl ester, previously obtained only in a yield of 0·1%, and now obtained in 31% yield. Pyrroporphyrin XV methyl ester, containing an unsubstituted β-position, has also been synthesised (27%).