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 b y the "3 +/- 1" methodology. 5-Nitroisoquinoline and 6-nitroquinoline conde nsed with ethyl isocyanoacetate in the presence of a phosphazene base to gi ve isoquino- and quinopyrroles, respectively. Ester saponification and deca rboxylation with KOH in ethylene glycol at 190 degreesC gave the parent aza tricycles, and these were further condensed with 2 equiv of an acetoxymethy lpyrrole to give the corresponding tripyrranes protected at the terminal po sitions as their tert-butyl eaters. In a one-pot procedure, the ester prote ctive groups were cleaved with TFA, and following dilution with dichloromet hane, "3 + 1" condensation with a pyrrole dialdehyde and dehydrogenation of the phlorin intermediate with DDQ gave the targeted azanaphthoporphyrins i n excellent yields. Although the UV-vis spectra of these new porphyrin syst ems are unexceptional, they show promise for further functionalization and applications in the development of porphyrin arrays. In addition, a zinc ch elate of the isoquinoporphyrin system shows a high degree of regioselective intermolecular interaction/aggregation in chloroform solution that may lea d to selectivity in molecular recognition studies.