Palladium(II)-Catalyzed Ortho Arylation of 2-Phenoxypyridines with Potassium Aryltrifluoroborates via C-H Functionalization

An efficient synthesis of ortho-arylated 2-phenoxypyridines catalyzed by palladium acetate is described. Treatment of 2-phenoxypyridines with two and a half equivalents of potassium aryltrifluoroborate and 10 mol % of Pd(OAc)(2) in the presence of two equivalents of Ag(2)CO(3), one equivalent of p-benzoquinone (BQ), and four equivalents of DMSO with (or without) H(2)O at 130-140 degrees C for 48 h in dried CH(2)Cl(2) gave the ortho-arylated 2-phenoxypyridines in modest to excellent yields. p-Benzoquinone is found to be an important ligand and co-oxidant for the transmetalation reductive elimination step in the catalytic reaction. The investigation of kinetic isotope effect (k(H)/k(D)) is determined to be 5.25, which indicates that C H bond cleavage occurs in the rate-determining step. One of the arylated compounds, 2-(4'-nitrobiphenyl-2-yloxy)pyridine, was treated with methyl trifluoromethanesulfonate and subsequently sodium methoxide to give the 2-(4-nitrophenyl)phenol in 79% yield, demonstrating that pyridine is a removable directing group.