To a mixture of 2-fluoro-5-(3-fluorophenyl)benzoic acid (intermediate III(a)) (632 mg, 2.7 mmol, 1.0 eq) and oxalyl chloride (1.03 g, 8.1 mmol, 3.0 eq) in DCM (30 mL) was added DMF (0.3 mL). The reaction mixture was stirred at room temperature for 1 h. The resulting mixture was concentrated to remove the solvent and excess oxalyl chloride then the residue obtained was dissolved in THF (20 mL). This solution was added dropwise to a suspension of 3-amino-2,4-dimethyl-phenol (370 mg, 2.7 mmol, 1.0 eq) and NaHCO3 (680 mg, 8.1 mmol, 3.0 eq) in THF (20 mL). After addition was complete, the reaction mixture was stirred at room temperature for 30 min. The resulting mixture was adjusted to pH 3 by addition of 1M HCl and the aqueous layer extracted with EtOAc. The organic extract was dried (Na2SO4), filtered, evaporated in vacuo and purified by column chromatography (EtOAc:petroleum ether, 0:1 to 1:1) to give the title compound as a yellow solid (400 mg, 42%).
