4-Nitrophenyl chloroformate (2) (492 mg, 2.44 mmol, 1.2 eq.) in dry THF (5 mL) was added slowly to an ice-cold solution of intermediate 1 (320 mg, 2.37 mmol, 1 eq.) in dry THF (15 mL) and pyridine (0.2 mL, 2.44 mmol, 1.2 eq.). The reaction was allowed to warm to room temperature and stirred overnight. The reaction mixture was evaporated to dryness, EtOAc was added, and the solution was washed with HCl (1 M, 15 mL) and brine (15 mL). The combined organic layers were dried over Na2SO4, filtered, and concentrated under reduced pressure. The crude product was purified by MPLC (EtOAc : hexane) to give the product as white solid (yield: 220 mg, 0.68 mmol, 33.8%); 1 General procedure for the preparation of final compounds 4-8.