Novel and Improved Syntheses of 5,15-Diphenylporphyrin and its Dipyrrolic Precursors
Bruckner, C., Posakony, J.J., Johnson, C.K., Boyle, R.W., James, B.R., and David Dolphin
J. Porphyrins and Phthalocyanines
Optimized syntheses of 5,15-diphenylporphyrin and its dipyrrolic precursors are described. A novel procedure for the synthesis of a dipyrromethane, prepared by hydrodesulfurization of the corresponding di-2-pyrrolylthione, is presented, as well as an improved method to isolate large quantities of 5-phenyldipyrromethane, prepared by the acid-catalysed condensation of pyrrole with benzaldehyde. These dipyrromethanes are key reagents in two high-yield (2+2)-type syntheses of DPP. 5-Phenyldipyrromethane was formylated to provide 1-formyl- and 1,9-diformyl-5-phenyldipyrromethane, and reduction provided the corresponding hydroxymethyl compound. These compounds, however, were much less efficient precursors to DPP. Two polypyrrolic compounds, 1,1,2,2-dipyrrolylethane and 5,10-diphenyltripyrrane, potentially useful for the synthesis of porphyrinic macrocycles, were isolated as side-products during the dipyrromethane and 5-phenyldipyrromethane syntheses.