Zwitterion: Important Tool for the Regioselective Synthesis of Five‑Membered Heterocycles: Mechanistic and Synthetic Perspectives

ABSTRACT Zwitterion intermediates have emerged as versatile tools for the regioselective synthesis of five‐membered heterocycles, advancing mechanistic understanding as well as practical possibilities in heterocyclic chemistry. This review delineates the diverse types of zwitterions and explores how these critically influence dipole moments, reactivity patterns, and synthetic utility. The manuscript systematically highlights in situ generation routes for zwitterions, such as base‐mediated deprotonation, nucleophilic addition, and cycloaddition reactions, with particular attention to pericyclic mechanisms and transition‐metal‐catalyzed [3+2] cycloadditions. Through mechanistic illustrations, the review showcases the roles of zwitterionic intermediates in constructing pyrazoles, oxadiazoles, imidazoles, pyrroles, furans, and thiophenes—each synthesized via pathways that enhance regioselectivity, minimize byproducts, and often proceed under mild, environmentally friendly conditions. The advantages of zwitterion‐based syntheses, such as operational simplicity, a broad substrate scope, and functional group tolerance, are juxtaposed with ongoing challenges in intermediate stabilization and selectivity control. Looking forward, the future perspective envisions that advances in zwitterion precursor design, catalytic system development, and integration into green chemistry will not only extend the reach of these strategies to new molecular targets but also catalyze innovations in pharmaceutical and materials science. Thus, zwitterionic intermediates are poised to remain at the forefront of sustainable, efficient, and inventive heterocyclic synthesis.