A Porphyrin with Two Coordination Sites: The Biquinoline Ligand as a New Potential External Chelate

A highly symmetrical doubly fused porphyrin was obtained after two successive intramolecular cyclizations. The first supplementary ring was closed by using the Cadogan reaction, involving the generation of an intermediate nitrene from the starting nitro function. By trying to use the same methodology for the second ring closure, we found that the Cadogan reaction could be used but that cyclization yields remained low. We showed, by taking into account unusual mass spectroscopy results, that the cyclization of the nitro functionality with the neighboring meso‐phenyl took place in the absence of the oxygen abstracting phosphite used by Cadogan. The bis‐biquinolino‐fused porphyrin, bearing an internal and an external coordination site, was obtained in very good yield and showed strong absorbance between 700 and 800 nm.