Phosgene (23 g, 232 mmol) was passed into ethyl acetate (250 ml) at 10° C. A solution of 2-amino-4,6-dimethoxypyrimidine (20 g, 129 mmol) and tributylamine (47.82 g, 258 mmol) in ethyl acetate (270 ml) was added dropwise in the course of 3 h. 15 min after the addition, the jacket was warmed to 30° C. and ethyl acetate and excess phosgene were distilled off in vac. The remaining solution of the isocyanate was cooled to 10° C. and added dropwise to a suspension of N,N-dimethyl-2-aminosulfonyl-4-nitro-benzamide (31.7 g, 116 mmol) and tributylamine (22.96 g, 232 mmol) in ethyl acetate (100 ml) at 20° C. in the course of 3 h. The mixture was stirred for 1 h and treated with water (300 ml) and potassium hydroxide solution (10% strength, 240 ml). After phase separation, the organic phase was extracted with water (50 ml). The combined aqueous phases were extracted with ethyl acetate (50 ml) and adjusted to pH 2 to 3 using 6M hydrochloric acid. After filtering off the product, washing with water (2×100 ml) and drying, 49.09 g (85.8% of theory) of N,N-dimethyl-2{-N-[N-(4,6-dimethoxypyrimidin-2-yl)aminocarbonyl]aminosulfonyl}-4-nitrobenz-amide were obtained.
