PURPURINS BEARING FUNCTIONALITY AT THE 6,16-MESO-POSITIONS - SYNTHESIS FROM 5,15-DISUBSTITUTED MESO-[BETA-(METHOXYCARBONYL)VINYL]PORPHYRINS

Porphyrins bearing p-X-phenyl substituents (X = Me, OH, OTs, NMe2, NO2) at the 5, 15-meso- positions have been synthesized. meso-Formylation of the nickel derivatives produced the derivatives (4), (12), (17) and (23) which show atypical broadened Soret and Q-band absorptions, the latter at 570-750 nm. The optical and n.m.r. spectra of the corresponding free base monoformyl derivatives also indicate electronic perturbations of the porphyrin 7T-system. Wittig reactions with (methoxycarbonylmethylene)triphenylphosphorane, followed by demetallation, resulted in the meso-acrylate porphyrins (8), (14), (19) and (25), which also exhibit unusual electronic spectra consistent with a distortion of the macrocydic ring current. The p-dimethylaminophenyl derivative (14) also shows protonation-dependent spectra indicating a quinomethene structure. The meso-acrylate porphyrins were efficiently converted into type A purpurins under basic conditions. Type B purpurins were also formed, and the relative yields of types A and B are temperature and solvent dependent, but independent of the presence of oxygen. These results are in contrast to those for the formation of octaethylpurpurin derivatives; likewise, no evidence of a purpurin-porphyrin equilibrium was observed for these compounds. In the presence of oxygen and strong visible light the meso-formyl-2-(methoxyoxalyl)chlorins are formed. The electronic spectra of the purpurins are typified by strong absorptions in the red region of the spectrum; the p-dimethylaminophenyl derivative (27) also exhibits a solvent-dependent spectrum, which is explained in terms of a dimethylaminoquinomethene tautomerism. The purpurins and porphyrin derivatives have potential application in photodynamic cancer therapy. © 1990 ASEG.