Monophosphaporphyrins: Oxidative π-Extension at the Peripherally Fused Carbocycle of the Phosphaporphyrin Ring

The 18π−σ3- and 22π−σ4-phosphaporphyrins were successfully prepared by an acid-promoted condensation between a phosphatripyrrane
and a 2,5-bis[hydroxy(phenyl)methyl]pyrrole, and their structures, aromaticity, and optical and electrochemical properties were disclosed.
Notably, a σ4-phosphaporphyrinogen and the 18π−σ3-phosphaporphyrin undergo oxidative π-extension at the peripherally fused carbocycle
to afford the 22π−σ4-phosphaporphyrin.