Recent Advances in Transition Metal-Free Halogenation of C(sp2)-H Bonds

C-X (X = halogen) bonds are indispensable functional groups in organic synthesis by mediating a massive number of important organic reactions. While a variety of different catalytic strategies are available for generating C-X bonds, those methods enabling the C-X bond formation under transition metal-free conditions via the C-H bond functionalization are particularly interesting because of the inherent atom economy and environmental friendliness associated with such methods. Herein, the advancements in the transition metal-free halogenation of C(sp²)-H bond are reviewed.