Acidolysis of intermediates used in the preparation of core-modified porphyrinic macrocycles

Abstract

The stability towards acidolysis of intermediates used in the preparation of core-modified porphyrinic macrocycles was examined. Experiments were performed using analogs of 5-phenyldipyrromethane in which one of the two pyrrole rings was modified (XPM). The XPMs utilized in these studies had X = 2-furyl (OPM), 2-thienyl (SPM), 2-selenyl (SePM), or 3-pyrrolyl (NCPPM). The XPMs possess a potentially labile linkage to a heteroatom-modified ring as well as a potentially labile linkage to a pyrrole ring. The stability of the two types of linkages was examined under acid catalysis conditions commonly used in the preparation of porphyrinic macrocycles. The methodology employed enabled characterization of the stability of the XPM (GC analysis), the yield of porphyrin (UV-vis absorption), and the composition of porphyrinic species (laser-desorption mass spectrometry, LD-MS) formed upon acidolysis of the XPM. These experiments showed that (1) the linkage to the heteroatom-modified ring is fairly stable in the presence of a linkage to pyrrole, and (2) the linkage to pyrrole is much more stable in the XPMs than is the case in 5-phenyldipyrromethane. Additional experiments with analogs of 5-phenyldipyrromethane having both rings modified ( X 2 M ), where X = 2- furyl ( O 2 M ), 2- thienyl ( S 2 M ), or 2- selenyl ( Se 2 M ) confirmed that linkages to furyl, thienyl, and selenyl rings are stable towards acidolysis. Taken together, the observations concerning stability of various linkages provide a foundation for understanding the types and yields of core-modified porphyrinic macrocycles formed in reactions with reactants that are not direct precursors to the isolated products.