The general procedure for the synthesis of pteridine-2,4-dione from 3-aminopyrazine-2-carbonitrile (1 mmol, 120 mg) and carbon dioxide was as follows: 3-aminopyrazine-2-carbonitrile (Compound 1d) and the ionic liquid [HDBN+][TFE-] (6 mmol, 1.35 g) were added to a 10 mL round bottom flask. The reaction mixture was heated to 90 °C under carbon dioxide atmosphere for 20 hours. After completion of the reaction, the system was cooled to room temperature and the pH was adjusted to neutral by adding saturated aqueous NH4Cl solution. The reaction mixture was extracted with dichloromethane (20 mL x 3), the organic phases were combined and dried over anhydrous sodium sulfate. After filtration, the organic phase was concentrated under reduced pressure. Purification by silica gel column chromatography (eluent ratio of dichloromethane:methanol=15:1) afforded a light yellow solid pteridine-2,4-dione (compound 2d, 141 mg) in 86% yield.
