3-Bromo-2,4-dimethylpyridine

108-47-4

27063-92-9

29976-20-3

27063-93-0

Under stirring, 2,4-dimethylpyridine (5.39 mL, 46.7 mmol, 1 equiv.) was dissolved in bromide (50 mL) containing 20% free SO3, keeping the reaction temperature at 0 °C. An efficient reflux condenser was installed and the reaction mixture was heated to 165 °C in an oil bath. Bromine (4.30 mL, 83.4 mmol, 0.9 eq.) was added slowly in 0.5 mL portions over a period of 5 hours and stirring was continued at 155-175 °C for 20 hours. After completion of the reaction, the solution was cooled to room temperature, poured onto crushed ice (200 g) and stirred for 1 hour. The resulting orange solution was neutralized by careful addition of solid Na2CO3, diluted with water and extracted with EtOAc (2 x 250 mL). The organic layers were combined, dried with Na2SO4 and concentrated in vacuum. The crude product was purified by automated fast column chromatography (Biotage KP-Sil.TM.SNAP 340g column, 0-15% EtOAc/hexane) and dried under vacuum to give three bromo products: 3,5-dibromo-2,4-dimethylpyridine (8), 5-bromo-2,4-dimethylpyridine (9) and 3-bromo-2,4-dimethylpyridine (10). 3,5-Dibromo-2,4-dimethylpyridine (8) is a white solid (1.48 g, 12%) with a melting point of 28-30 °C; 1H NMR (400 MHz, CDCl3) δ 2.54 (s, 3H, CH3), 2.61 (s, 3H, CH3), 8.41 (s, 1H, pyHortho); 13C NMR (100 MHz, CDCl3) δ 23.8 (CH3), 25.7 (CH3), 120.3 (ArC), 124.4 (ArC), 146.4 (ArC), 148.5 (ArCH), 156.5 (ArC); IR νmax (film)/cm1 3045, 2998, 2956, 2921, 1558, 1433, 1376, 1349, 1232, 1376, 1349, 1232, 1232, 1232, 1232, 1232, 1232, 1232, 1232, 1232, 1232, 1232, 1232, 1232, 1232, 1232, 1232, 1232, 1232 1376, 1349, 1232, 1049, 993, 928, 783; HRMS (ESI+) m/z calcd for C7H8Br2N [M+H]+ 263.9018, found 263.9027. 5-Bromo-2,4-dimethylpyridine (9) was a colorless oil (1.89 g, 22%); 1H NMR (400 MHz, CDCl3) δ 2.32 (s, 3H, CH3), 2.44 (s, 3H, CH3), 7.00 (s, 1H, pyHortho), 8.47 (s, 1H, pyHmeta); 13C NMR ( 100 MHz, CDCl3) δ 22.1 (CH3), 23.6 (CH3), 120.4 (ArC), 125.5 (ArCH), 146.7 (ArC), 150.5 (ArCH), 157.0 (ArC); IR νmax (film)/cm1 2985, 2957, 2924, 2854, 1592, 1461, 1377 1592, 1461, 1377, 1353, 1289, 1177, 1032; HRMS (ESI+) m/z calcd for C7H9BrN [M+H]+ 185.9913, found 185.9918. 3-Bromo-2,4-dimethylpyridine (10) was a colorless oil (3.04 g, 35%); 1H NMR (400 MHz, CDCl3) δ 2.33 (s, 3H, CH3), 2.61 (s, 3H, CH3), 6.91 (d, J = 5.0 Hz, 1H, pyHmeta), 8.18 (d, J = 5.0 Hz, 1H, 2995, 2958, 2922, 1585, 1437, 1389, 1123, 1024, 916, 825; HRMS (ESI+) m/z calcd for C7H9BrN [M+H]+ 185.9913, found 185.9917.