General procedure for the synthesis of 6-chloro-7H-purin-8(9H)-ones from 6-chloropyrimidine-4,5-diamine and N,N'-carbonyldiimidazole: 6-chloropyrimidine-4,5-diamine (7.46 mmol, 1.08 g), 1,1'-carbonyldiimidazole (2 equiv, 14.92 mmol, 2.42 g) and 1,4-dioxane (20 mL) were mixed. It was heated and refluxed under nitrogen protection for 50 min. Upon completion of the reaction, the yellow solution was concentrated to an oil. Dichloromethane (80 mL) was added and allowed to stand for 1 h. The solid product was filtered, collected and dried in a vacuum oven at 45 °C to give 6-chloro-7H-purin-8(9H)-one (1.22 g, 7.15 mmol, 96% yield). Mass spectrum (electrospray positive ion mode): m/z = 169 ([M+H]+).
