[F:1][C:2]1[C:10]([CH3:11])=[CH:9][CH:8]=[CH:7][C:3]=1[C:4]([OH:6])=[O:5].S(=O)(=O)(O)O.[CH3:17]O>>[F:1][C:2]1[C:10]([CH3:11])=[CH:9][CH:8]=[CH:7][C:3]=1[C:4]([O:6][CH3:17])=[O:5]To a solution of 2-fluoro-3-methyl benzoic acid (3.57 g, 23 mmol) in MeOH (40 mL) was added concentrated sulfuric acid (2.3 mL), and the reaction mixture was heated at reflux for 12 h. The reaction mixture was cooled, the solvent was removed under reduced pressure, and the residue was dissolved in EtOAc. The organic solution was washed with a saturated solution of NaHCO3 and then brine, dried (Na2SO4), filtered and concentrated under reduced pressure to afford methyl 2-fluoro-3-methylbenzoate as a yellow oil (3.2 g, 82%): 1H NMR (300 MHz, CDCl3) δ 7.76-7.71 (m, 1H), 7.39-7.34 (m, 1H), 7.08 (t, J=8 Hz, 1H), 3.98 (s, 3H), 2.31 (d, J=3 Hz, 3H).
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