D-Camphorsulfonic Acid → 5-Bromo-3-(4-(1-ethyl-3-oxopiperazin-2-yl)phenylamino]-ethylpyrazin-2(1H)-one

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A 100-mL single-neck round-bottomed flask equipped with a magnetic stirrer and reflux condenser was charged with 33 (450 mg, 2.05 mmol), isopropanol (5 mL), 13 (603 mg, 2.26 mmol) and DL-10-camphorsulfonic acid (813 mg, 3.50 mmol), and the reaction mixture was then stirred at reflux for 16 h. After this time, the reaction mixture was cooled to room temperature, filtered and the filter cake washed with isopropanol (10 mL). The resulting solid was dissolved in methylene chloride/methanol (3:1), absorbed onto silica gel and purified by flash chromatography to afford 34 in 79% yield (654 mg) as an orange solid: mp 152-153° C.; 1H NMR (500 MHz, CDCl3) 8.28 (bs, 1H 7.73 (d, 2H, J=8.5 Hz), 7.43 (d, 2H, J=8.5 Hz), 6.74 (s, 1H), 5.90 (d, 1H, J=3.5 Hz), 4.12 (s, 1H), 3.60 (m, 1H), 3.52 (s, 3H), 3.36 (m, 1H), 3.12 (m, 1H), 2.60 (m, 2H), 2.28 (m, 1H), 1.00 (t, 3H, J=7.0 Hz); MS (ESI+) m/z 406.0 (M+H).

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