[F:1][C:2]1[CH:10]=[CH:9][C:5]([C:6]([OH:8])=[O:7])=[CH:4][C:3]=1[CH:11]=[O:12].CI.[C:15]([O-])([O-])=O.[K+].[K+]>CN(C=O)C.CCOC(C)=O.O>[CH3:15][O:7][C:6](=[O:8])[C:5]1[CH:9]=[CH:10][C:2]([F:1])=[C:3]([CH:11]=[O:12])[CH:4]=1To a solution of 4-fluoro-3-formyl-benzoic acid (800 mg, 4.8 mmol) in DMF (10 mL), are added MeI (0.35 mL, 5.7 mmol) and K2CO3 (790 mg, 5.7 mmol). The reaction mixture is stirred at room temperature for 18 hours. The reaction mixture is diluted with EtOAc (20 mL) and water (10 mL). The organic layer is separated, washed with brine, dried under anhy. Na2SO4 (500 mg), filtered and is concentrated. The residue is purified by silica gel flash chromatography with 0-20% EtOAc/heptane as the eluent. The product fractions are collected and concentrated to afford 4-fluoro-3-formyl-benzoic acid methyl ester (710 mg, 82%).
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