[C:1]([O:5][C:6](=[O:17])[C:7]1[CH:12]=[CH:11][C:10]([CH2:13]Br)=[C:9]([F:15])[C:8]=1[F:16])([CH3:4])([CH3:3])[CH3:2].C[N+]([O-:22])(C)C>CS(C)=O.C(Cl)Cl>[C:1]([O:5][C:6](=[O:17])[C:7]1[CH:12]=[CH:11][C:10]([CH:13]=[O:22])=[C:9]([F:15])[C:8]=1[F:16])([CH3:4])([CH3:3])[CH3:2]To a solution of 4-bromomethyl-2,3-difluoro-benzoic acid tert-butyl ester (12.9 g, 42.1 mmol) in DMSO (80 mL) and DCM (40 mL) at 0° C. was added trimethylamine N-oxide (3.4 g, 45.3 mmol). The reaction mixture was stirred at room temperature for 18 hours before being concentrated in vacuo. The resultant residue was partitioned between iced water and ethyl acetate. The organic layer was separated and washed with brine twice, dried (Na2SO4), filtered and evaporated in vacuo. The resultant residue which was subjected to flash chromatography (Si—PPC, gradient 0% to 10%, TBME in cyclohexane) to afford the title compound as a white solid (4.34 g, 43%). 1H NMR (CDCl3, 400 MHz) 10.38 (1 H, d, J=0.8 Hz), 7.71 (1 H, dddd, J=7.4, 5.6, 1.7, 0.8 Hz), 7.63 (1 H, ddd, J=7.4, 5.6, 1.5 Hz), 1.61 (9 H, s).
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