To a solution of 2,3-dimethyl-5-phenyl-benzoic acid (315 mg, 1.4 mmol, 1.1 eq) in CH2Cl2 (10 mL) was added oxalyl chloride (530 mg, 4.2 mmol, 3.3 eq) at 0° C. The reaction was allowed to warm to room temperature and stirred for 1 h. The solvent and excess reagent were removed under reduced pressure and the residue that remained dissolved in THF (10 mL) and added dropwise to a mixture of 3-amino-2,4-difluoro-phenol (intermediate X(a)) (184 mg, 1.3 mmol, 1.0 eq) and NaHCO3 (532 mg, 6.3 mmol, 5.0 eq) in THF (8 mL) at 0° C. The reaction was stirred at room temperature for 2 h, water was added and the aqueous layer was extracted with EtOAc. The combined organic extracts were washed with water and brine, dried (Na2SO4), filtered, and evaporated in vacuo. The residue was purified by column chromatography (petroleum ether:EtOAc, 20:1 to 10:1, then CH2Cl2:MeOH, 500:1 to 100:1) to give the title compound as a yellow solid (220 mg, 49%).
