Copper‐Catalyzed Arylation of Nitrogen Heterocycles from Anilines under Ligand‐Free Conditions

The arylation of pyrazole and derivatives can be achieved by coupling arenediazonium species (formed in situ from anilines) by using a catalytic system that employs low-toxicity and inexpensive copper metal under very mild and ligand-free conditions (T=20 °C). From other nitrogen heterocycles, the presence of an additive (NBu4 I) significantly improves the efficiency of the catalytic system. These results represent the first examples of CN bond formation from arenediazonium species.