Mechanochemical Rhodium(III)‐Catalyzed CH Bond Functionalization of Acetanilides under Solventless Conditions in a Ball Mill

In a proof‐of‐principle study, a planetary ball mill was applied to rhodium(III)‐catalyzed C? H bond functionalization. Under solventless conditions and in the presence of a minute amount of Cu(OAc)₂, the mechanochemical activation led to the formation of an active rhodium species, thus enabling an oxidative Heck‐type cross‐coupling reaction with dioxygen as the terminal oxidant. The absence of an organic solvent, the avoidance of a high reaction temperature, the possibility of minimizing the amount of the metallic mediator, and the simplicity of the protocol result in a powerful and environmentally benign alternative to the common solution‐based standard protocol.