A solution of 3.55 g of ethyl 3-amino-4,4,4-trifluorocrotonate in 50 ml of n-hexane is added dropwise while stirring at 0°-3° C. during 15 minutes to 0.85 g of a 55% sodium hydride dispersion in 50 ml of dimethylformamide and the mixture is stirred for 30 minutes. A solution of 5.0 g of isopropyl 2-chloro-4-fluoro-5-isocyanatobenzoate in 100 ml of n-hexane is subsequently added dropwise during 5 minutes while stirring and cooling at -15° C. The temperature of the reaction mixture rises to 10° C. and the mixture is thereafter stirred at room temperature for one hour. The intermediate isopropyl 2-chloro-4-fluoro-5-[3-(2-ethoxycarbonyl -1-trifluoromethyl-vinyl)ureido]-benzoate which thereby separates is not isolated.
