To a solution of phenol 4 (3.0 g, 9.88 mmol) in DMF (20 mL) were added TBDMSCl (1M in CH2Cl2, 20 mL, 19.8 mmol), imidazole (2.1 g, 29.6 mmol) and DMAP (0.25 g, 1.98 mmol) at room temperature. The mixture was stirred at ambient temperature for 14 hours. The mixture was extracted with EtOAc/H2O (75 mL/250 mL). The organic layer was dried over MgSO4, filtered, and concentrated in vacuo. The residue was purified by silica column chromatography (Biotage) to provide the title compound 21 (4.12 g, 99%).
