Palladium-Ruthenium Catalyst Complementarity Strengthens Ortho-Directed C-H Bond Arylation Of 2-Arylpyrazines

We report the Pd- or Ru-catalyzed C-H bond arylation at the ortho-position of the aryl unit of 2-arylpyrazines. The reaction proceeds with complete regioselectivity using phosphine-free Pd(OAc)(2) or [RuCl2(p-cymene](2) as the catalysts and potassium acetate as an inexpensive base. In all cases, the mono-arylation of 2-arylpyrazines was obtained even with 2,3-diphenylpyrazine. Moreover, the reaction is not sensitive to the pyrazine substitution. By selecting the proper catalytic system, a wide variety of electron-rich and -poor (hetero)aryl bromides, including bromopyridine derivatives, has been successfully employed.