(7r)-2-Chloro-8-cyclopentyl-7-ethyl-7,8-dihydro-6(5H)-pteridinone (260 mg, 0.93 mmol) was dissolved in dioxane (5 ml). Trimethyl phosphate (650 mg, 4.6 mmol) and potassium carbonate (192 mg, 1.39 mmol) were added and the reaction mixture was stirred at 90 °C for 6 hours until the ingredients were completely consumed. After completion of the reaction, the mixture was diluted with water and extracted with ethyl acetate. The organic phase was dried over anhydrous sodium sulfate and concentrated under reduced pressure, and the residue was purified by silica gel column chromatography (petroleum ether: ethyl acetate = 1:1) to afford (7R)-2-chloro-8-cyclopentyl-7-ethyl-7,8-dihydro-5-methyl-6(5H)-pteridinone as a white solid (270 mg, 86% yield).1H NMR (CDCl3) δ: 7.7 (s 1H), 4.34 (m, 1H), 4.25 (m, 1H), 3.33 (s, 3H), 2.1-1.6 (m, 10H), 0.86 (t, 3H).
