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A solution of Intermediate 56 (0.92 g, 3.3 mmol) in dichloromethane was treated successively with tert-butyldimethylsilyl chloride (0.75 g, 5.0 mmol), DMAP (50 mg), and triethylamine (1.4 mL, 10 mmol). After a few minutes, additional quantities of tert-butyldimethylsilyl chloride (0.75 g, 5.0 mmol) and triethylamine (1 mL) were added. The mixture was filtered through a pad of Celite and concentrated. The residue was purified via automated flash silica gel chromatography, using a 40 g Silicycle SiliSep flash column (hexanes/ethyl acetate). Concentration of the desired fractions under reduced pressure provided the title compound as clear, colorless syrup (0.99 g, 76%). ES/MS calcd. for C23H44NO2Si+ 394.3. Found m/z=394.4 (M+H)+.

1. waitAfter a few minutes
2. filtrationThe mixture was filtered through a pad of Celite
3. concentrationconcentrated
4. customThe residue was purified via automated flash silica gel chromatography