Cyclization Through Dual C(sp³)–H Functionalization

C(sp³)−H functionalization methods have been widely employed in many organic transformations such as cyclization reactions, heterocycle synthesis, cross‐coupling protocols, and photochemical transformations. Among these transformations, cyclization reaction through C(sp³)−H functionalization offers a direct route to convert simple linear substrates to complex products. There are three common modes of utilizing C(sp³)−H bonds in cyclization reactions including single, double, and dual C(sp³)−H functionalization. As the most challenging mode, dual C(sp³)−H functionalization refers to converting two separate C(sp³)−H bonds in one molecule into desired C−Z bonds which can be employed in cyclization reactions. Cyclization reaction via dual functionalization of C(sp³)−H bonds can be classified based on the C−H reactivities. Therefore, these reactions can be categorized into three classes based on the types of C(sp³)−H bonds including activated‐activated, activated‐unactivated, and unactivated‐unactivated C(sp³)−H bonds. Most published reports for cyclization reactions through dual C(sp³)−H functionalization involve activated‐activated C(sp³)−H bonds. However, the number of reported papers on the other two classes has been growing. This review focuses on the dual C(sp³)−H functionalization protocols used for cyclization reactions and categorizes the published papers based on the types of C(sp³)−H bonds.