2-Amino-5-bromo-4-chlorophenol (Intermediate 7, 8.4 g, 37.8 mmol) and N,N'-carbonyldiimidazole (12.2 g, 75.6 mmol) were used as raw materials and reacted in THF (250 mL) for 3 hours at 80 °C. After completion of the reaction, the solvent was removed by distillation under reduced pressure. The crude product was purified by silica gel column chromatography (200-400 mesh, 100 g) with petroleum ether/ethyl acetate as eluent (gradient from 9:1 to 5:1) to afford 6-bromo-5-chlorobenzo[d]oxazol-2(3H)-one as an orange solid (7.7 g, 82% yield).LCMS (Method A): retention time 1.49 min, molecular ion peak m/z 248 /250 [M+H]+.
