N[C:2]1[C:3]([CH3:13])=[CH:4][C:5]([Br:12])=[C:6]([CH:11]=1)[C:7]([O:9][CH3:10])=[O:8].N([O-])=O.[Na+].[ClH:18]>O.[Cu]Cl>[Br:12][C:5]1[CH:4]=[C:3]([CH3:13])[C:2]([Cl:18])=[CH:11][C:6]=1[C:7]([O:9][CH3:10])=[O:8]To a solution of methyl 5-amino-2-bromo-4-methylbenzoate (4.86 g, 20 mmol) in hydrochloric acid (6N, 50 mL) was added sodium nitrite (1.38 g, 20 mmol) carefully at −5° C. After one hour, the obtained mixture was added to a boiling solution of copper(I) chloride (3.96 g, 40 mmol) in water (50 mL) dropwise and the resulting mixture was refluxed with stirring for 2 h. The mixture was cooled to rt and extracted with ethyl acetate (2×50 mL). The combined organic layers were washed with brine, dried over Na2SO4, filtered and concentrated. The residue was purified by silica gel column chromatography eluted with PE to give methyl 2-bromo-5-chloro-4-methylbenzoate (3.4 g, yield 64.4%). 1H NMR (400 MHz, DMSO-d6): δ 7.82 (s, 1H), 7.81 (s, 1H), 3.85 (s, 3H), 2.51 (s, 3H) ppm; MS: m/z=265.0 (M+1, ESI+).
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