Porphyrins with Exocyclic Rings. 15. Synthesis of Quino- and Isoquinoporphyrins, Aza Analogues of the Naphthoporphyrins

Porphyrins with fused isoquinoline and quinoline units have been prepared by the “3 + 1” methodology. 5-Nitroisoquinoline and 6-nitroquinoline condensed with ethyl isocyanoacetate in the presence of a phosphazene base to give isoquino- and quinopyrroles, respectively. Ester saponification and decarboxylation with KOH in ethylene glycol at 190 °C gave the parent azatricycles, and these were further condensed with 2 equiv of an acetoxymethylpyrrole to give the corresponding tripyrranes protected at the terminal positions as their tert-butyl esters. In a one-pot procedure, the ester protective groups were cleaved with TFA, and following dilution with dichloromethane, “3 + 1” condensation with a pyrrole dialdehyde and dehydrogenation of the phlorin intermediate with DDQ gave the targeted azanaphthoporphyrins in excellent yields. Although the UV−vis spectra of these new porphyrin systems are unexceptional, they show promise for further functionalization and applications in the development of porphyrin arrays. In addition, a zinc chelate of the isoquinoporphyrin system shows a high degree of regioselective intermolecular interaction/aggregation in chloroform solution that may lead to selectivity in molecular recognition studies.