Synthesis and reactivity of 10,15,20-triaryl-5-oxaporphyrin copper complexes

5-Oxaporphyrin copper complexes having phenyl, 4-methoxycarbonylphenyl, and 4-chlorophenyl in the meso positions were prepared by oxidation of copper bilatrienones with H2O2 or meta-chloroperoxybenzoic acid in the presence of trifluoroacetic acid. The yields were 78% (COOMe), 88% (H) and 43% (Cl). The 5-oxaporphyrin copper complex is a cationic species and exhibited a more positive (ca. 0.7 V) redox potential than copper tetraphenylporphyrin. Quantum mechanical calculations revealed that it has a low LUMO level of −3.2 eV. The meso-aryl-5-oxaporphyrin copper complex underwent alcoholysis to yield 19-alkoxybilinone. Nucleophilic ring-opening of the 5-oxaporphyrin copper complexes with OH−, CH3O−, and C2H5O− gave bilindione, 19-methoxybilinone, and 19-ethoxybilinone, respectively, indicating that they are valuable precursors of linear tetrapyrroles.