56
J. Setsune
Fig. 3.8 Synthesis of A-type, A 2 -type, and AB-type porphyrins
to various meso-substituted porphyrins. cis-A 2 -type meso-diarylporphyrins 22 was
synthesized by the 3+1 condensation of tripyrrane 21, pyrrole, and aromatic aldehyde in the molar ratio of 1:1:2, for example, 5,10-diphenylporphyrin was prepared
in 6% yield. The 2+1+1 condensation of 2-hydroxymethylpyrrole, 17, and aromatic
aldehyde gave A-type meso-arylporphyrins 20 that can be converted into cis-ABtype meso-diarylporphyrins 23 by nucleophilic addition of organolithium reagents
(Ryppa et al. 2005).
Porphyrin meso-positions undergo ordinary electrophilic substitution reactions
such as formylation, nitration, halogenation, and so on. Furthermore, various
substituents can be introduced into the meso-position of porphyrin by means of
transition metal-catalyzed cross-coupling reactions (Fig. 3.9) (Senge 2011; Ryan
et al. 2011). trans-AB-type meso-diarylporphyrins 19 was readily brominated to
Fig. 3.9 Post-introduction of meso-substituents into porphyrin