Recent advances in directing group rearrangement strategies in transition-metal-catalyzed C-H activation

After more than two decades of continuous development, transition-metal-catalyzed C-H activation cascade reactions have gradually become an important methodology and strategy for the construction of complex molecules. This transformation is typically achieved by installing a functional group with a directing effect onto the substrate to enable C-H activation at a specific site. Such directing groups must possess adequate coordination ability, oxidation capability, and transformability. In most reported reactions, C-H activation occurs first, followed by the participation of the directing group in subsequent transformations to enable the efficient construction of complex frameworks. In these cases, the directing group is generally retained in the product molecule in a relatively intact form. However, a few examples have shown that the directing group can be cleaved via a rearrangement strategy or rearranged into a less intact form within the product. Based on an analysis of the reported examples, the coupling reagents employed in transition-metal-catalyzed C-H activation cascade reactions have evolved from simple alkenes and alkynes to a diverse array of functionalized derivatives. In addition, diazo compounds and ylides, which combine both stability and reactivity, have also emerged as valuable coupling partners. Even unstable triazenes derivatives can be successfully employed in this type of transformation. This review mainly summarizes the literature reported prior to 2026 and concludes with a foreseeable bright outlook for the field.