Pictet-Spengler Synthesis of N-heteroaromatics Extended Porphyrins

Porphyrins are highly conjugated heterocyclic compounds and are found as the backbone of many natural products such as heme and chlorophyll. To improve its biological and optical properties, the functionalization of porphyrin at its β- and meso-position has gained importance in recent years.The purpose of this review is to describe the Pictet-Spengler method for the incorporation of nitrogenous and biologically important heterocyclic scaffolds such as pyrrolo-/indolo[1,2-a]quinoxaline, pyrrolo[1,2-a]pyrazine, and quinoline at the β- and meso-positions of the porphyrins to increase π-conjugation and improve their biological, optical, and electrochemical properties.This review provides a comprehensive overview of the synthesis of N-heterocyclic extended porphyrins and metalloporphyrins via a modified Pictet-Spengler approach. The synthesized porphyrins were found to be highly conjugated and exhibited improved photophysical properties compared to their parent analogues. Moreover, the review article provided a brief overview of the Pictet-Spengler procedure, including product yields, reaction conditions, photophysical properties of the synthesized products, and potential applications in a variety of fields.