Oxidation of 5,15‐Dioxaporphyrin: Its Generality and Novelty as an Oxaporphyrin Analogue

Abstract

Abstract5,15‐Dioxaporphyrin (DOP) is a novel meso‐oxaporphyrin analogue and exhibits unique 20π‐antiaromaticity, unlike its mother congener of 18π‐aromatic 5‐oxaporphyrin, commonly known as its cationic iron complex called verdohem, which is a key intermediate of heme catabolism. To reveal its reactivities and properties as an oxaporphyrin analogue, the oxidation of tetra‐β‐arylated DOP (DOP‐Ar4) was explored in this study. Stepwise oxidation from the 20π‐electron neutral state was achieved, and the corresponding 19π‐electron radical cation and 18π‐electron dication were characterized. Further oxidation of the 18π‐aromatic dication resulted in the formation of a ring‐opened dipyrrindione product by hydrolysis. Considering a similar reaction of verdoheme to ring‐opened biliverdin in the heme degradation in nature, the current result consolidates the ring‐opening reactivity of oxaporphyrinium cation species.