[Br:1][C:2]1[C:3]([O:11][CH3:12])=[CH:4][C:5]([F:10])=[C:6]([CH:9]=1)C=O.O.C1(C)C=CC(S(O)(=O)=O)=CC=1.[CH:25]([O:30][CH3:31])([O:28][CH3:29])OC.C(N(CC)CC)C>CO.[Cl-].[Na+].O.C(OCC)(=O)C>[CH3:31][O:30][CH:25]([O:28][CH3:29])[C:6]1[CH:9]=[C:2]([Br:1])[C:3]([O:11][CH3:12])=[CH:4][C:5]=1[F:10]5-Bromo-2-fluoro-4-methoxybenzaldehyde (1 g, 4.3 mmol), p-toluenesulfonic acid monohydrate (163 mg, 0.86 mmol) and trimethyl orthoformate (2.4 mL, 21 mmol) were dissolved in methanol (20 mL) and stirred under heating and reflux for 1 hour. After standing to cool the reaction mixture, triethylamine (2 mL) was added thereto and further stirred for 10 minutes. The mixture was added with saturated brine and ethyl acetate, and the organic layer was separated, followed by washing with saturated brine. The organic layer was dried over anhydrous magnesium sulfate and the solvent was evaporated under reduced pressure to obtain 5-bromo-2-fluoro-4-methoxybenzaldehyde dimethylacetal (1.19 g, 100%).
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