[Synthesis]
To a cooled solution of diisopropylamine (20.4 g, 28.0 mL, 0.202 mol) in anhydrous THF (400 mL) at -78 °C was slowly added n-BuLi (0.192 mol, 58.0 mL, 3.3 M hexane solution). The reaction mixture was stirred at -78 °C for 1 h, followed by the dropwise addition of anhydrous THF (150 mL) solution of 2-bromopyridine (25.3 g, 0.160 mol) over 20 min. After keeping the reaction at -78 °C for 90 min, an anhydrous THF (25 mL) solution of DMF (35.0 g, 0.480 mol) cooled to -78 °C was quickly added. Stirring was continued at -78 °C for 80 min, and upon completion of the reaction, the reaction was quenched with NaH2PO4 (27.6 g, 0.230 mol, dissolved in H2O (120 mL)), slowly warmed to room temperature, and diluted with MeOt-Bu (500 mL). The organic phase was separated, washed with brine (2100 mL), dried over anhydrous Na2SO4 and concentrated under reduced pressure. The crude product was ground with pentane and after decantation, the remaining solid was recrystallized from hexane to give 16.7 g of 2-bromo-3-pyridinecarboxaldehyde as a pale yellow solid in 56% yield, melting point 67-69 °C. 1H NMR (400 MHz, CDCl3) δ: 10.35 (s, 1H), 8.57 (dd, J=4.7,2.1 Hz, 1H), 8.17 (dd, J= 7.6,2.1Hz, 1H), 7.44 (dd, J=7.6,4.7,0.6Hz, 1H).13C NMR (101MHz, CDCl3) δ: 190.4,154.0,144.9,137.5,130.1,123.0. Calculated values for elemental analyses (C6H4BrNO): C, 38.74; H. 2.17; N, 7.53; Br, 42.96. Measured values: C, 38.58; H, 2.08; N, 7.57; Br, 42.69. |
[References]
[1] Tetrahedron Letters, 2008, vol. 49, # 17, p. 2839 - 2843
[2] Chemical Communications, 2011, vol. 47, # 23, p. 6635 - 6637
[3] Organic Letters, 2007, vol. 9, # 5, p. 891 - 894
[4] Tetrahedron Letters, 2017, vol. 58, # 20, p. 1989 - 1991
[5] Synthesis (Germany), 2018, vol. 50, # 1, p. 155 - 169 |