M. Koley, N. Dastbaravardeh, M. Schnürch, M.D. Mihovilovic:
"Palladium(II)-Catalyzed Regioselective Ortho Arylation of sp2 C-H Bonds of N-Aryl-2-amino Pyridine Derivatives";
The direct arylation of N-(2-pyridyl) substituted anilines is described. Arylation takes place in ortho position to the amine functionality and is directed by the pyridine N-substituent. Remarkably, N-arylation was never obsd. as a competing process even though conditions also suitable for Buchwald-Hartwig reactions were applied. The scope of the reaction was investigated in terms of aryl donors as well as the electronic nature of the substrate. Good yields were obtained for most examples through an operationally simple procedure, which did not require inert conditions or even glove box techniques. Pd(OAc)2 was applied as a cheap catalyst and boronic acids as readily available aryl donors. To obtain full conversion, 1,4-benzoquinone and a silver salt (e.g., Ag2O) were required as additives and reacted at relatively mild temps. (e.g., 80 °C). Addnl., the pyridine-directing group was cleaved after the reaction to give ortho-arylated aniline derivs.
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