A solution of 3.6 g of isopropyl 2-chloro-4-fluoro-5-(1,2,4,5,6,7-hexahydro-2,4-dioxo-3H-cyclopenta[d]pyrimidin-3-yl)-benzoate in 50 ml of absolute dimethylformamide is stirred at room temperature for 2 hours with 0.43 g of a 55% sodium hydride dispersion. A solution of 0.93 g of acetyl chloride in 10 ml of absolute dimethylformamide is subsequently added dropwise during 10 minutes and the mixture is stirred for 2 hours. The reaction mixture is dissolved in 100 ml of ethyl acetate and the solution is washed thoroughly with water. The organic phase is dried over anhdrous sodium sulphate and evaporated to dryness. The residue is purified by chromatography on a silica gel column using methylene chloride/ethyl acetate (3:1) as the eluent. There is obtained isopropyl 2-chloro-4-fluoro-5-(1,2,4,5,6,7-hexahydro-1-acetyl-2,4-dioxo-3H-cyclopenta[d]pyrimidin-3-yl)-benzoate, 1H--NMR (CDCl3, 400 MHz) 7.86 ppm (d, 1H), 7.37 ppm (d, 1H), 5.24 ppm (m, 1H), 3.13 ppm (m, 2H), 2.75 ppm (m, 2H), 2.68 ppm (s, 3H), 2.12 ppm (m, 2H), 1.36 ppm (d, 6H).
