[Synthesis]
To a cold solution of oxime 11 (8 g, 33.19 mmol) in dichloromethane (200 mL) was added 2,6-dimethylpyridine (4.5 mL, 38.8 mmol) at 0 °C, followed by slow dropwise addition of trifluoromethanesulfonic anhydride (5.6 mL, 33.34 mmol). After removing the cooling bath, the reaction mixture was heated to reflux and maintained for 3 hours. Upon completion of the reaction, the mixture was cooled to room temperature and DBU (9.9 mL, 66.3 mmol) was added slowly and dropwise while the internal temperature of the reaction was controlled to not exceed 30°C. Stirring was continued at room temperature for 1 h. Subsequently, the mixture was poured into an excess of dilute sodium bicarbonate solution under vigorous stirring. After stirring for a few minutes, the organic layer was separated. The aqueous layer was extracted twice with dichloromethane (100 mL x 2). The organic extracts were combined, dried with magnesium sulfate and concentrated to give a dark brown solid. The solid was purified by short silica gel column chromatography using pure dichloromethane as eluent. The collected grades were dried under vacuum, ground with dichloromethane/hexane (1:4, 50 mL), and the resulting solid was filtered and dried under vacuum to give 5.36 g (82% yield) of the final light yellow solid product.12 IR (KBr) νmax/cm-1 : 3436, 3310 (NH2), 3032 (Ar-H), 2920 ( Aliphatic-H), 2246 (CN), 1610, 1512, 1418 (C=C).1H NMR (500MHz, CDCl3) δ: 4.47 (br.s, 2H, NH2); 6.88 (dd, 1H, J=2.8, 8.2Hz, H-5); 6.94 (br.s, 1H, H-3); 7.24 (d, 1H, J=8.2 Hz, H-6).13C NMR (125.7 MHz, CDCl3) δ: 95.17 (C-1), 117.16 (CN), 118.15 (C-3), 121.60 (C-5), 129.03 (C-4), 133.60 (C-6), 150.47 (C-2). Calculated elemental analysis (%) C7H5BrN2 (195.96): C 42.67, H 2.56, N 14.22; measured values (%): C 42.60, H 2.61, N 14.17. |