Intramolecular NN Bond Formations to Access N‐Heterocycles Under Transition Metal‐Free Conditions

Discovery of versatile approaches for the construction of high‐valued N‐rich heterocycles has been a very important research topic in organic chemistry for several years. Owing to their widespread applications in natural products, pharmaceuticals, dye industry, and materials, a multitude of efficient methods to access N‐heterocyclic scaffolds have been uncovered. Of them, transition metal‐free intramolecular NN bond‐forming strategies are distinctive category of transformations and highly preferred because of their wider scope and versatility. In this review, we summarized the existing literature to access N‐heterocycles involving transition metal‐free intramolecular NN bond‐forming approaches from 2015 to 2025. Methodological advancements reported under (1) electrochemical, (2) photochemical, (3) I 2 ‐promoted, (4) hypervalent iodine‐mediated, and (5) N‐halo succinimide‐based conditions are explored. Reaction conditions, representative examples, limitations, post‐synthetic applications, and mechanism are discussed wherever applicable. We expect that the synthetic approaches discussed herein will serve as a comprehensive reference tool and enable further expansion in this field.