Aryl DiazoniumSalt-TriggeredCyclization and Cycloaddition Reactions: Past, Present, and Future

Aryl diazonium salts occupy a privileged role in synthetic chemistry owing to their ready availability and versatile reactivity. While their applications in accessing diversely functionalized arene derivatives via denitrogenation-coupling and reduction/addition reactions have been well recognized by practitioners in both academia and industry, recent renaissance in chemical transformations of retaining the key N-2-unit has emerged as a powerful technique to construct variousN-heterocycles. This review covers the history and latest advances in cyclization and cycloaddition reactions using aryl diazonium salts as N-2-annulation synthons. The scope, applications, and opportunities in exploring new chemical space by this sustainable strategy are summarized and discussed.