[F:1][C:2]1[CH:3]=[C:4]([N+:19]([O-:21])=[O:20])[C:5]([O:17]C)=[C:6]([C:8]2[CH:13]=[CH:12][CH:11]=[C:10]([C:14]([OH:16])=[O:15])[CH:9]=2)[CH:7]=1>Br>[N+:19]([C:4]1[C:5]([OH:17])=[C:6]([C:8]2[CH:13]=[CH:12][CH:11]=[C:10]([C:14]([OH:16])=[O:15])[CH:9]=2)[CH:7]=[C:2]([F:1])[CH:3]=1)([O-:21])=[O:20]5′-Fluoro-2′-methoxy-3′-nitro-biphenyl-3-carboxylic acid 2d (2.91 g, 10.0 mmol) was dissolved in 10 mL of hydrobromic acid (40%). The reaction mixture was heated to reflux at 120° C. overnight. The reaction was monitored by TLC until the disappearance of the starting materials. The mixture was concentrated under reduced pressure and the resulting residue was purified by silica gel column chromatography to obtain the title compound 3′-nitro-5′-fluoro-2′-hydroxy-biphenyl-3-carboxylic acid 2e (2.38 g, yield 85.7%) as a yellow solid, which was directly used in the next step.
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