The Evolving Enantioselective C─H Functionalization of Tertiary Allylic Systems

The direct functionalization of tertiary and other inert allylic C─H bonds represents one of the most attractive strategies in the construction of complicated molecules with quaternary carbon centers. Unlike approaches that rely on pre‐functionalized allylic substrates, such as halides, acetates, and carbonates, allylic C─H activation provides an atom‐ and step‐economical route to forge diverse and valuable C─C and C─X bonds. Although the functionalization of secondary allylic C─H bonds has been extensively studied and well established in recent years, the corresponding transformation of tertiary allylic C─H bonds remains considerably underdeveloped. This concept summarizes the progress and mechanistic pathways—including transition‐metal insertion (via two‐electron transfer) and radical‐involving single‐electron transfer processes—enabling the functionalization of various tertiary allylic C─H bonds. Future directions in this long‐standing and challenging field are also discussed.