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

• Published in: Organometallics Vol. 29; no. 18; pp. 4058 - 4065
• Main Authors: Chu, Jean-Ho, Lin, Pi-Shan, Wu, Ming-Jung
• Format: Journal Article
• Language: English
• Published: WASHINGTON American Chemical Society 27.09.2010; Amer Chemical Soc
• Subjects: Chemistry; Chemistry, Inorganic & Nuclear; Chemistry, Organic; Physical Sciences; Science & Technology; ROOM-TEMPERATURE; PALLADIUM; CROSS-COUPLING REACTIONS; MECHANISM; ALKYLATION; BOND ACTIVATION; SP; DERIVATIVES; ARYL CHLORIDES; CATALYZED DIRECT ARYLATION
• ISSN: 0276-7333; 1520-6041
• DOI: 10.1021/om100494p

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 Ag2CO3, one equivalent of p-benzoquinone (BQ), and four equivalents of DMSO with (or without) H2O at 130−140 °C for 48 h in dried CH2Cl2 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.