To a solution of chiral 5-bromo-1-((2R,3R,4S,5S)-3,5-difluoro-4-hydroxy-5-hydroxymethyl-3-methyl-tetrahydro-furan-2-yl)-1H-pyrimidine-2,4-dione (50 mg, 0.14 mmol) prepared in Preparation 7 in THF (3 ml) at 0° C. was added a THF solution (Aldrich, 1 M) of tert-butylmagnesium chloride (0.35 mL, 0.35 mmol) dropwise. The mixture was stirred at 0° C. for 15 min, followed by the addition of THF solution (0.5 M) of (2S)-isopropyl 2-(chloro(naphthalen-1-yloxy)phosphorylamino)propanoate prepared in Example 2 Step B (0.7 mL, 0.35 mmol). The reaction mixture was warmed to room temperature and stirred for 2 h. Methanol (2 mL) was added to quench the reaction. The mixture was purified by flash chromatography (5-10% MeOH in DCM) to give (S)-2-[[(2S,3S,4R,5R)-5-(5-bromo-2,4-dioxo-3,4-dihydro-2H-pyrimidin-1-yl)-2,4-difluoro-3-hydroxy-4-methyl-tetrahydro-furan-2-ylmethoxy]-(naphthalen-1-yloxy)-phosphorylamino]-propionic acid isopropyl ester as a white solid (50 mg, 52%).
