Cyclization Through Dual C(sp3)-H Functionalization

C(sp(3))-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(sp(3))-H functionalization offers a direct route to convert simple linear substrates to complex products. There are three common modes of utilizing C(sp(3))-H bonds in cyclization reactions including single, double, and dual C(sp(3))-H functionalization. As the most challenging mode, dual C(sp(3))-H functionalization refers to converting two separate C(sp(3))-H bonds in one molecule into desired C-Z bonds which can be employed in cyclization reactions. Cyclization reaction via dual functionalization of C(sp(3))-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(sp(3))-H bonds including activated-activated, activated-unactivated, and unactivated-unactivated C(sp(3))-H bonds. Most published reports for cyclization reactions through dual C(sp(3))-H functionalization involve activated-activated C(sp(3))-H bonds. However, the number of reported papers on the other two classes has been growing. This review focuses on the dual C(sp(3))-H functionalization protocols used for cyclization reactions and categorizes the published papers based on the types of C(sp(3))-H bonds.