To a solution of 25 (0.12 g, 0.62 mmol, 1.0 equiv) in anhydrous dimethylformamide (3 mL) was added imidazole(0.11 g, 1.55 mmol, 2.5 equiv) and t-butyldimethylsilyl chloride (0.11 g, 0.74 mmol, 1.2 equiv) at 23 Celsius. After stirring at this temperature for 30 min, the mixture was diluted with ethyl acetate (25 mL) and washed with brine(10 mL x 5), dried over anhydrous sodium sulfate, filtered, concentrated, and purified by silica gel column chromatography (6% ethyl acetate – hexanes) to give 118 as a colorless oil (0.15 g, 81%).