To a solution of 4-[2-(3-bromo-4-chloro-benzoylamino)-3-methyl-phenoxy]-butyric acid tert-butyl ester (10.2 g, 21.3 mmol) in dry DMF (100 mL) at 0° C. under N2, NaH (60% in mineral oil, 1.7 g, 42.6 mmol) was added in several portions with stirring. 10 minutes later, iodomethane (2.0 mL, 32.1 mmol) was added. The mixture was warmed to room temperature by removal of ice bath and stirring was continued for 1 hr. Water (10 mL) was then added and organics were extracted by ethyl acetate, which was then washed by water and brine, and was dried over MgSO4. After concentration, the crude product was purified by silica gel chromatography eluting with ethyl acetate/hexane (1/4) to yield 4-{2-[(3-bromo-4-chloro-benzoyl)-methyl-amino]-3-methyl-phenoxy}-butyric acid tert-butyl ester (9.5 g).
