[F:1][C:2]1[CH:7]=[CH:6][C:5]([C:8]2[CH:9]=[C:10]([CH:13]=[CH:14][C:15]=2[O:16]C)[CH:11]=[O:12])=[CH:4][C:3]=1[S:18]([CH3:21])(=[O:20])=[O:19].B(Br)(Br)Br.CO>C(Cl)Cl>[F:1][C:2]1[CH:7]=[CH:6][C:5]([C:8]2[CH:9]=[C:10]([CH:13]=[CH:14][C:15]=2[OH:16])[CH:11]=[O:12])=[CH:4][C:3]=1[S:18]([CH3:21])(=[O:19])=[O:20]To a cooled solution (0° C.) of 3-(4-fluoro-3-(methylsulfonyl)phenyl)-4-methoxybenzaldehyde (27) (400 mg, 1.3 mmol, 1 eq.) in DCM (20 mL) was added BBr3 (0.4 mL). The reaction mixture was stirred room temperature for 3 h. After cooling to 0° C., methanol was added and the mixture was concentrated under vacuum. The residue was diluted with DCM and washed with water. The DCM was dried (Na2SO4) and concentrated in vacuo. The residue was purified by column chromatography (eluent: PE:EA=1:1) to give 340 mg (89%) of 3-(4-fluoro-3-(methylsulfonyl)phenyl)-4-hydroxybenzaldehyde (28).
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