To a solution of 5-(3,5-difluorophenyl)-2,3-dimethyl-benzoic acid (240 mg, 0.92 mmol, 1.1 eq) in CH2Cl2 (12 mL) was added (COCl)2 (348 mg, 2.75 mmol, 3.3 eq) and DMF (5 drops). The reaction mixture was stirred at room temperature for 1.5 h, then concentrated under reduced pressure to remove the organic solvent and excess reagent. The residue obtained was dissolved in THF (10 mL) and added dropwise to a solution of 3-amino-2,4-difluorophenol (intermediate X(a)) (121 mg, 0.83 mmol, 1.0 eq) and NaHCO3 (386 mg, 4.6 mmol, 5.0 eq) in THF (10 mL) at 0° C. After the addition, the reaction mixture was stirred at room temperature for 1 h. The resulting mixture was diluted with water and extracted with EtOAc. The organic extract was washed with water and brine, dried (Na2SO4), filtered and evaporated in vacuo. The residue was purified by column chromatography (CH2Cl2:MeOH, 500:1 to 200:1) to give the title compound as a yellow solid (50 mg, 15%).
