Conjugated macrocycles related to the porphyrins .6. Oxypyriporphyrin, the first fully aromatic porphyrinoid macrocycle with a pyridine subunit

The synthesis of the first example of an aromatic pyridine-containing porphyrinoid 10 has been accomplished in excellent yields by the acid-catalyzed ''3+1'' condensation of 3-hydroxypyridinedicarboxaldehyde (8) with tripyrrane 9. The key intermediate 8 was obtained by the selenium dioxide oxidation of the known biscarbinol 7. The aromaticity of ''oxypyriporphyrin'' 10 has been confirmed by MS, NMR, IR, and UV/Vis spectroscopy. This system afforded a monocation in 0.2% TFA-chloroform, and a dication was observed in 2% TFA-chloroform; these species also retained macrocyclic aromaticity. Oxypyriporphyrin readily formed the corresponding metal chelates 14a-c by reaction with zinc, copper(II), or nickel(II) acetate, and this observation suggests that there are extensive possibilities for the use of 10 in coordination chemistry. Oxypyriporphyrin and the related semiquinone system oxybenziporphyrin represent the first two members of a new class of aromatic porphyrinoids.