Novel and improved syntheses of 5,15-diphenylporphyrin and its dipyrrolic precursors

Optimized syntheses of 5,15-diphenylporphyrin (DPP, 1) and its dipynolic pr ecursors are described. A novel procedure for the synthesis of dipyrrometha ne (2), prepared by hydrodesulfurization of the corresponding di-2-pyrrolyl thione (8), is presented, as well as an improved method to isolate large qu antities of 5-phenyldipyrromethane (4), prepared by the acid-catalysed cond ensation of pyrrole with benzaldehyde. These dipyrromethanes are key reagen ts in two high-yield (2+2)-type syntheses of DPP. 5-Phenyldipyrromethane wa s formylated to provide 1-formyl- (11) and 1,9-diformyl-5-phenyldipyrrometh ane (12), and reduction of 11 provided the corresponding hydroxymethyl comp ound 13, These compounds (11-13), however, were much less efficient precurs ors to DPP. Two polypyrrolic compounds, 1,1,2,2-dipyrrolylethane (9) and 5, 10-diphenyltripyrrane (10), potentially useful for the synthesis of porphyr inic macrocycles, were isolated as side-products during the dipyrromethane and 5-phenyldipyrromethane syntheses. (C) 1998 John Wiley & Sons, Ltd.