Preparation of Six Isomeric Bis-acylporphyrins with Chromophores Reaching the Near-Infrared via Intramolecular Friedel−Crafts Reaction

We describe the preparation of six diketones based on the frameworks of five bis-naphthoporphyrins
and one perinaphthoporphyrin. All diketones derive from meso-tetraarylporphyrins having
incorporated two carbonyl groups, each one connected to one β-pyrrole carbon and one ortho carbon
atom from a meso-aryl group. These compounds were all produced in good yield by intramolecular
Friedel−Crafts acylation, either from porphyrins meso-substituted by o-carboxyphenyl or o,o‘-dicarboxyphenyl substituents or from porphyrins bearing carboxy groups attached to the pyrrolic
β-positions. Although the former reaction does not show significant regioselectivity when run on
nickel complexes, the opposite is true for the corresponding free bases. All diketones show a
spectacular bathochromic shift of the UV−vis absorption, the longest wavelength bands absorbing
in the 700−825 nm range. Two compounds were structurally characterized by X-ray diffraction. In
the case of the diketone, whose carbonyl groups are attached to vicinal pyrrolic β-positions, a
significant intermolecular interaction between the two carbonyl groups and an aromatic hydrogen
atom was detected.