Synthesis and Properties of 5,15-Dioxaporphyrin Bearing Various meso-Aryl Substituents

Herein, a scope of meso-substituents for the synthesis of 5,15-dioxaporphyrins (DOPs), a novel antiaromatic porphyrinoid, was investigated. DOPs with various types of aryl substituents were synthesized by nucleophilic aromatic substitution reaction of nickel bis(α,α’-dibromodipyrrin) complexes bearing corresponding meso-aryl substituents and subsequent intramolecular annulation reaction of β-hydroxy-substituted intermediates. Using a copper dipyrrin complex instead of nickel complexes, a copper complex of DOP was synthesized for the first time. The meso-substituents did not significantly alter the antiaromaticity of DOPs but affected crystal packing diagrams and oxidation behaviors; DOPs with less sterically hindering para-substituted phenyl or 2-thienyl substituents formed mutual stacking in the crystal structures, whereas the covalently β-β linked dimer species was generated during the electrochemical oxidation of those kinds of DOPs.