Synthesis, Characterization, and Electrochemical Studies of New π‐Extended Metalloporphyrins

A doubly fused porphyrin has been synthesized by two successive cyclization reactions. The first meso‐phenyl group was fused by an intramolecular Cadogan reaction leading to an enamine‐functionalized porphyrin. After Vilsmeier–Haack formylation of the nickel enaminoporphyrin, an intramolecular Friedel–Crafts reaction followed by dehydration of the intermediate alcohol afforded the doubly fused aromatic nickel porphyrin, which could be demetalated. The free base and the copper and palladium porphyrins show extremely high absorbances in the 700–800 nm range. The palladium complex was a good catalyst for the oxidation of cholesterol with singlet oxygen, which makes this chromophore a potential candidate for photodynamic therapy.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)