Reaction Steps
A solution containing quinoxaline (15.6 g), 120 mmol) and iodine (30.5 g, 120 mmol) in CF2ClCFCl2 (150 ml) was placed in a fluorination apparatus fitted with a drying tube filled with soda lime. Elemental fluorine (165 mmol) as a 10% mixture in nitrogen was then passed through the stirred solution using narrow bore PTFE tubing at ca. 40 ml/min. After the fluorine had been added the solution was poured into 10% aqueous sodium metabisulfite solution (300 ml), neutralised with sodium bicarbonate and continuously extracted with dichloromethane for 24 hours. The organic extracts were dried and evaporated to an oil (13.6 g). GC/MS analysis showed a 49% conversion of quinoxaline. The oil was purified by column chromatography on silica gel using dichloromethane as eluant to give pure 2-fluoroquinoxaline as a pale yellow oil (5.30 g, 62% based on 49% conversion); RF 0.53; δH (200 MHz; CDCl3 ; Me4Si) 7.7 ppm (2H, m), 7.9 (1H, m), 8.1 (1H, m), 8.67 (1H, d, JH,F 7.9, H-3); δF (250 MHZ; CDCl3 ; Me4Si) -75.1 ppm (s); δC (50.3 MHz, CDC13, Me4Si) 128.4 ppm (d, 4JC,F 1.6, C-8), 129.4 (s, C-7), 129.45 (s, C-6), 131.6 (s, C-5), 136.5 (d, 2JC,F 42.6, C-3), 139.72 (d, 3JC,F 10.9, C-8a), 141.52 (d 4JC,F 1.8, C-4a), 156.74 (d, 1JC-F 256.0, C-2); m/z (E1+) 148 (M+, 100), 129 (20), 121 (12), 103 (17), 76 (24), 50 (17); and 2,3-difluoroquinoxaline (0.27 g, 3%) as a pale yellow solid; RF 0.75; δH (400 MHz, CDCl3, Me4Si) 7.79 ppm (2H, m, Ar-H), 7.99 (2H, m, Ar-H); δC (50 MHz, CDCl3, Me4Si) 127.8 (s, C-8), 130.4 (s, C-7), 130.4 (s, C-7), 138.4 (d d, 3JC-F 5.4, C-4a), 146.1 (d d, 1JC-F 261.3,2JC-F 39.5, C-2); δF (235 MHz, CDCl3, CFCl3) -82.8 ppm (s); m/z (E1+) 166 (M+, 100%), 139 (11).
