The 1,5-Benzodiazepin-2-Ones: A Review on Synthetic Strategies, Reactivity and Functional Applications

1,5-Benzodiazepin-2-one is a significant class of heterocyclic compounds that have attracted considerable attention due to these versatile scaffolds and their multifunctional properties. Owing to the presence of a fused benzene–diazepine core, these compounds display rich chemical reactivity and various physicochemical characteristics, making them valuable structures in both fundamental and applied research. This review provides a comprehensive and critical overview of the advances reported to date on 1,5-benzodiazepin-2-ones, with particular emphasis on their diverse synthetic methodologies, reaction mechanisms, and structure–property relationships. Classical and modern synthetic approaches are discussed, including condensation reactions, multicomponent processes, catalytic and green chemistry approaches, as well as recent developments toward more sustainable and efficient protocols. The intrinsic reactivity of the 1,5-benzodiazepin-2-one framework enables access to structurally diverse derivatives. Furthermore, the review summarizes the broad range of applications of these heterocycles, especially in medicinal chemistry, where they have demonstrated significant biological activities, as well as in corrosion inhibition and photoluminescent materials. Finally, current challenges, limitations, and future perspectives are outlined to provide guidance for further research and development of 1,5-benzodiazepin-2-one-based systems.