Photo- and electro-chemical synthesis of substituted pyrroles

Pyrrole, a privileged five-membered nitrogen-containing heterocycle, widely exists in the structures of various natural products, therapeutic agents, functional materials, and catalysts for organic synthesis, among others. Over centuries, continuous attention from the synthetic community has been focused on the development of efficient methods for pyrrole synthesis. As enabling methodologies for sustainable organic synthesis, both photochemical and electrochemical methods have garnered growing research attention in recent decades, offering new avenues for the construction of substituted pyrroles from diverse N-containing precursors via distinct mechanism patterns. This review critically summarizes the methodological advancements in both photo- and electro-chemical pyrrole synthesis, and categorizes them based on the utilized N-containing precursors, including (1) 2H-azirines, (2) vinyl azides, (3) primary amines, (4) enamines, (5) tetrahydroisoquinolines, (6) N-propargylindoles, (7) malononitriles, (8) α-amino acids, and (9) miscellaneous precursors, to reveal the current status and trends of this area. The representative scopes and mechanism patterns of these protocols are highlighted, aiming to inspire innovations in future methodology discoveries to address the challenges in modern pyrrole synthesis.