Cyclization Through Dual C(sp3)−H Functionalization

Abstract 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.