Palladium-on-Carbon-Catalyzed Coupling of Nitroarenes with Phenol: Biaryl Ether Synthesis and Evidence of an Oxidative-Addition-Promoted Mechanism

Nucleophilic substitution in nitroarenes to form biaryl ethers is of fundamental importance in organic synthesis. Under non‐catalytic conditions, this can occur if highly activated nitroarenes are used or if the nucleophile is activated by a strong stoichiometric base. We established a new method involving the use of a ligand‐free palladium‐on‐carbon (Pd/C) catalyst for the cross‐coupling of activated nitroarenes with relatively non‐nucleophilic phenol derivatives, including naphthol, in the absence of harsh bases. Control experiments, hot filtration, the three‐phase test, and inductively coupled plasma atomic emission spectroscopy analysis revealed that the catalysis proceeded through an usual oxidative addition step of the nitroarene to Pd/C, which resulted in the release of active palladium particles having extremely high catalytic activity. DFT calculations revealed the origin of the selectivity of the activated nitroarenes.