Cyclization Reactions of <i>N</i>‐Aminopyridinium Salts: Synthetic Scope and Mechanistic Insights

N ‐Aminopyridinium salts are readily available and bench‐stable nitrogen‐containing precursors that have demonstrated broad synthetic utility in diverse cyclization reactions. As practical 1,3‐dipoles, N ‐aminopyridinium salts can engage with dipolarophiles in cycloaddition reactions to construct nitrogen‐containing heterocycles. Moreover, as a class of novel aminating or bifunctional aminating reagents, they are capable of generating nitrogen‐centered radicals under visible‐light irradiation, which can initiate amination‐cyclization processes. In recent years, cyclization strategies involving N ‐aminopyridinium salts have made remarkable progress and garnered significant attention. This review highlights recent advances in the cyclization chemistry of N ‐aminopyridinium salts and their derivatives, with a particular focus on transition‐metal catalyzed, transition‐metal‐free systems and visible‐light‐induced transformations. The scope, limitations, and synthetic applications of various cyclization strategies are critically discussed, aiming to reveal the innovative potential of N ‐aminopyridinium salts as nitrogen‐based precursors in synthetic chemistry. We hope this review provides valuable insights and inspiration for future research in synthetic methodology, drug discovery, and the design of functional materials.