Palladium-Catalyzed Chelation-Assisted Aromatic C–H Nitration: Regiospecific Synthesis of Nitroarenes Free from the Effect of the Orientation Rules

A palladium-catalyzed chelation-assisted ortho-nitration of aryl C–H bond is described. A
range of azaarenes
such as 2-arylquinoxalines, pyridines, quinoline, and pyrazoles were
nitrated with excellent chemo- and regioselectivity. Using the O-methyl oximyl group as a removable directing group, the
regiospecific synthesis of a variety of o-nitro aryl
ketones was achieved starting from aryl ketones via a three-step process
involving the Pd-catalyzed ipso-nitration of C–H
bond as a key step. Mechanistic investigations support a silver-mediated
radical mechanism involving Pd­((II/III) and/or Pd­(II/IV) catalytic
cycles under oxidizing conditions.