To the crude 9 (72.1 mmol, 1 eq) dissolved in dry DMF (1500 mL) under argon at 0° C. was added sodium hydride (10.7 g, 446.8 mmol, 6.2 eq). After 15 min, were added dropwise benzyl bromide (54 mL, 454 mmol, 6.3 eq) and a catalytic amount of potassium iodide. The mixture was stirred at room temperature for 3 h, diluted with water (500 mL) and Et2O (600 mL). The aqueous phase was extracted with Et2O (3×300 mL). The organic extracts were combined, dried over MgSO4 and concentrated. Purification by flash chromatography on silica gel (petroleum ether/EtOAc 90:10) afforded 10 as viscous syrup (27.5 g, 60% over 2 steps).
