To a 500 mL of dry round-bottomed flask were added (2R,3R,4R,5R)-5-(2-amino-6-chloro-9H-purin-9-yl)-2-(benzoyloxymethyl)-4-fluoro-4-methyltetrahydrofuran-3-yl benzoate (6a, 8.0 g, 15.2 mmol) and anhydrous benzyl alcohol (128 mL). To another 250 mL of dry round-bottomed flask were charged NaH (60% in mineral oil, 2.44 g, 60.8 mmol) and anhydrous DMF (40 mL). The suspension was stirred at 0° C. in an ice-water bath. Benzyl alcohol (27 mL) was added drop-wise via a syringe. A solution was slowly formed and it was transferred to the nucleoside suspension quickly under a nitrogen atmosphere at room temperature. The mixture was heated to 50° C. and stirred. The reaction was complete after 3 h and cooled to ambient temperature. It was neutralized by the addition of 4 N HCl to ca. pH=7 (12 mL). The solution was concentrated under reduced pressure (4 mbar, 90° C. bath). The cloudy residue was diluted with dichloromethane (100 mL) and washed with water (3×30 mL), brine (30 mL) and dried over Na2SO4. The suspension was filtered and the filtrate was concentrated under reduced pressure to an oily residue. This was purified by column chromatography (Analogix, 0 to 8% gradient of MeOH in DCM). The product eluted at 4% MeOH in DCM. The product containing fractions were combined, concentrated under reduced pressure and dried (50° C., 0.2 mmHg, 17 h) to a white foam solid (4.57 g, 11.7 mmol, 77.2%).
