7-Fluoro-1,3-dihydro-2H-indol-2-one (1.0 g) is introduced as initial charge in 10 ml of N,N-dimethylacetamide. A solution of potassium carbonate (1.8 g) and potassium hydroxide (0.3 g) in 10 ml of water is added and the mixture is briefly after-stirred. Then, a solution of 2-chloro-4,6-diethoxy-1,3,5-triazine (3.0 g, ca. 50% purity) in 10 ml of N,N-dimethylacetamide, and 10 ml of water are added. A solid separates out from the clear yellow solution. The mixture is stirred at room temperature and further 2-chloro-4,6-diethoxy-1,3,5-triazine (1 g, ca. 50% purity) is added in two portions after 2 and 18 hours. The mixture is stirred for a further 3 hours at 30° C., admixed with 10 ml of toluene, adjusted to pH 1-2 with hydrochloric acid (10%) and after-stirred for 30 min. The solid is filtered off with suction, washed twice alternately with water and heptane and dried. This gives the title compound as solid in an HPLC purity of 99% area (1.53 g, 72% of theory).
