To a suspension of sodium hydride (2.77 g, 69.2 mmol) in anhydrous ethanol (150 mL) was added 2,4-diamino-6-chloropyrimidine (5.0 g, 34.6 mmol) in batches. The reaction mixture was heated to reflux and kept for 6 hours. After completion of the reaction, it was cooled to room temperature and the reaction solution was neutralized with an isopropanol solution of 5-6 N hydrochloric acid. The solvent was removed by concentration under reduced pressure and the resulting residue was purified by silica gel column chromatography (eluent: dichloromethane/methanol=40:1, v/v) to afford 2,4-diamino-6-ethoxypyrimidine as a white solid (4.0 g, 75% yield). The melting point of the product was 164-165 °C. 1H NMR (300 MHz, DMSO-d6, 25 °C): δ 6.00 (s, 2H, NH2), 5.88 (s, 2H, NH2), 5.03 (s, 1H, CH), 4.13 (q, J=7.1 Hz, 2H, OCH2CH3), 1.22 (t, J=7.1 Hz, 3H OCH2CH3).13C NMR (75 MHz, DMSO-d6, 25°C): δ 170.0 (C), 165.9 (C), 162.9 (C), 76.1 (CH), 60.2 (OCH2CH3), 14.7 (OCH2CH3). High resolution mass spectrometry (HRMS): calculated value C6H11N4O [M+H]+ 155.09329, measured value 155.09260.
