Recent advances in C-H functionalization of 2-indazoles.

2-Indazoles are one class of the most important nitrogen-containing heterocyclic compounds. The 2-indazole motif is widely present in bioactive natural products and drug molecules that exhibit distinctive bioactivities. Therefore, much attention has been paid to access diverse 2-indazole derivatives. Among them, the late-stage functionalization of 2-indazoles C-H activation is recognized as an efficient approach for increasing the complexity and diversity of 2-indazole derivatives. In this review, we summarized recent achievements in the late-stage functionalization of 2-indazoles, including the C3-functionalization of 2-indazoles through transition metal-catalyzed C-H activation or a radical pathway, transition metal-catalyzed C2'-H functionalization of 2-indazoles and remote C-H functionalization at the benzene ring in 2-indazoles.