Diethyl chlorophosphate → [5-Fluoro-2-(4-fluorobenzyloxy)pyrimidin-4-yl]phosphoramidic acid diethyl ester

To a magnetically stirred solution of 5-fluoro-2-(4-fluorobenzyloxy)pyrimidin-4-ylamine (0.10 g, 0.42 mmol) in dry THF (5 mL) under a nitrogen atmosphere was added NaH (0.017 g of a 60 wt. % suspension, 0.42 mmol) and the mixture was stirred until bubbling ceased. Diethyl chlorophosphate (0.073 g, 0.42 mmol) was added dropwise, and the mixture was stirred at ambient temperature for 1 h. The reaction mixture was evaporated to dryness and the residue dissolved in EtOAc and washed saturated aqueous NH4Cl solution. The organic layer was separated, dried over Na2SO4, filtered, and evaporated. The crude material was purified on silica (acetone/CH2Cl2 gradient) to give 0.017 g (11%) of [5-fluoro-2-(4-fluorobenzyloxy)pyrimidin-4-yl]phosphoramidic acid diethyl ester as a white solid: mp 109-111° C.; 1H NMR (300 MHz, CDCl3) δ8.10 (t, J=1.8 Hz, 1H), 7.43 (m, 2H), 7.03 (t, J=8.5 Hz, 2H), 6.18 (br s, 1H), 5.35 (s, 2H), 4.25 (m, 4H), 1.38 (t, J=7.1 Hz, 6H); HPLC-MS (ESI) m/z 374 (M+H)+.