[C:1]([C:3]1[CH:4]=[CH:5][C:6]([F:11])=[C:7]([CH:10]=1)[CH:8]=[O:9])#[N:2].OO.Cl([O-])=[O:15].[Na+]>O.C(#N)C>[C:1]([C:3]1[CH:4]=[CH:5][C:6]([F:11])=[C:7]([CH:10]=1)[C:8]([OH:15])=[O:9])#[N:2]NaH2PO4 (87 mg, 0.724 mmol) in water (3.5 mL) was added to a solution of 5-cyano-2-fluorobenzaldehyde (500 mg, 3.35 mmol) in acetonitrile (7 mL), followed by 30% H2O2 (0.31 mL). Sodium chlorite (434 mg, 4.8 mmol) in water (3.5 mL) was added dropwise to this reaction mixture at 0° C. The mixture was stirred at room temperature for 1 h, quenched with aqueous sodium sulfite solution at 0° C. and then acidified with 1.5N HCl solution. The aqueous solution was extracted with EtOAc and the combined extracts were dried over anhydrous sodium sulfate, and concentrated under reduced pressure to afford 5-cyano-2-fluorobenzoic acid (500 mg, yield 90%). 1H NMR (300 MHz, DMSO-d6) δ 13.79 (br s, 1H), 8.30-8.27 (dd, J=6.6 Hz, 2.2 Hz, 1H), 8.17-8.12 (ddd, J=8.6 Hz, 4.4 Hz, 2.3 Hz, 1H), 7.60-7.53 (dd, J=10.5 Hz, 8.8 Hz, 1H). MS (ESI) m/z: Calculated for C8H4FNO2: 165.02. found: 163.6 (M−H)−.
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