Into a homogeneous solution of 1-(3,5-dichloro-4-hydroxyphenyl)-3-(2,6-difluorobenzoyl)urea (3.13 grams, 8.66 mmol) in dimethylformamide (25 milliliters) was added triethylamine (1.75 grams, 17.3 mmol), and the resulting mixture was stirred for 5 minutes. Tertiary-butyldimethylsilyl chloride (3.92 grams, 26.0 mmol) was then added, and a thick precipitate formed immediately. This heterogeneous mixture was then diluted with ethyl acetate (200 milliliters), washed with saturated sodium bicarbonate (twice with 150 milliliters) and then washed with a brine solution (150 milliliters). The organic layer was dried over sodium sulfate, filtered, and concentrated under reduced pressure to give a brown solid. The solid was washed with cold ether and vacuum dried to afford 1-(4-tert-butyldimethylsiloxy-3,5-dichlorophenyl)-3-(2,6-difluorobenzoyl)urea (2.71 grams, 5.70 mmol) having a melting point of 184° C.-186° C. Elemental analysis of the product indicated the following:
