Unusual phlorins from the oxidative coupling of pentapyrromethanes:: their facile conversion to meso-substituted porphyrins

Direct, oxidant-mediated intramolecular coupling of pentapyrromethanes afforded 5-aryl-5-(2 ' -pyrryl)-10,15,20-triaryl-porphyrin (phlorins) as single products. The outcome of the reaction is comparable with the oxidative coupling of tetra-pyrromethanes. Treatment of obtained phlorins with trifluoroacetic acid resulted in exclusive elimination of the peripheral pyrrole affording mwso-tetraarylporphyrins quantitatively. The rate of pyrrole elimination depends on the acid concentration. The selective binding with fluoride anion was also observed with a large association constant. (C) 2001 Published by Elsevier Science Ltd.