[CH:1]([C:3]1[CH:4]=[C:5]([CH:9]=[CH:10][CH:11]=1)[C:6]([OH:8])=[O:7])=[O:2].[Br:12]N1C(=O)CCC1=O>OS(O)(=O)=O>[CH:1]([C:3]1[CH:4]=[C:5]([CH:9]=[C:10]([Br:12])[CH:11]=1)[C:6]([OH:8])=[O:7])=[O:2]A solution of 3-formyl-benzoic acid (10.8 g) in H2SO4 (100 mL) is warmed to 60° C. before N-bromo-succinimide (13.4 g, 75.5 mmol) was added in 3 portions every 15 min. After complete addition, stirring was continued for 2 h at 60° C. The mixture is poured onto 1000 g of ice. The precipitate that formed was collected, washed with water and dried under high vacuum to give 3-formyl-5-bromo-benzoic acid as a white powder (15.1 g). LC-MS*: tR=0.39 min, [M+H]+=227.03.
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