Aromatic and nonaromatic pyriporphyrins.

Pyriporphyrins with three different orientations for the pyridine moiety have been prepared using a '3 + 1' strategy. The nonaromatic pyriporphyrins are stable so long as phenyl substituents are present at the meso-positions adjacent to the pyridine ring. An aromatic dihydropyriporphyrin with an external CO2Ph protective group has also been prepared from 2,4-pyridinedicarbaldehyde.