Monophosphaporphyrins: oxidative pi-extension at the peripherally fused carbocycle of the phosphaporphyrin ring.

The 18pi-sigma3- and 22pi-sigma4-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 sigma4-phosphaporphyrinogen and the 18pi-sigma3-phosphaporphyrin undergo oxidative pi-extension at the peripherally fused carbocycle to afford the 22pi-sigma4-phosphaporphyrin.