Lithium hexamethyldisilazane → 4-Fluoro-2-(2-fluoro-4-methylsulfanyl-phenylamino)-3-formyl-benzoic acid

To a cold (−78° C.) solution of 2-fluoro-4-methylsulfanyl-phenyl amine (1.55 g, 9.9 mmol) in THF (15 mL) was added LHMDS (9.9 mL, 1.0 M solution in hexanes 9.9 mmol) dropwise so as to maintain the temperature below −65° C. After stirring for 30 minutes a solution of 3-dimethoxymethyl-2,4-difluoro-benzoic acid (700 mg, 3.0 mmol) in THF (15 mL) was added dropwise, the resultant mixture stirred cold for 3 hours then allowed to warm to room temperature and stirred for 18 hours. The reaction was quenched by the addition of aqueous ammonium chloride and the products partitioned between ethyl acetate and water. The aqueous layer was separated and acidified to pH 1 (concentrated HCl) and then extracted twice with ethyl acetate. The combined organic extracts were dried (Na2SO4), filtered and concentrated in vacuo. The resultant residue was triturated with diethyl ether to give the title compound as a yellow solid (105 mg, 10% yield). 1H NMR (CDCl3, 400 MHz) 10.26-10.23 (2 H, m), 8.04 (1 H, dd, J=8.76, 6.31 Hz), 7.03-6.96 (2H, m), 6.91 (1 H, d, J=1.96 Hz), 6.65 (1 H, dd, J=10.02, 8.77 Hz), 2.42 (3 H, s).