Compound 4 (3 g, 6.60 mmol) was dissolved in THF (30 mL), Et3N (1.11 mL, 7.92 mmol) and Ac2O (742 mg, 7.26 mmol) were added at RT. The reaction mixture was stirred at RT for 2 h. The volatiles were evaporated under reduced pressure and the residue obtained was diluted with CH2Cl2 and washed with dilute HCl. The combined organic extracts were dried over Na2SO4 and concentrated under reduced pressure. The crude residue was purified by column chromatography using 30% EtOAc/Hexane as eluent to yield compound 5 (2.5 g, 76%).
