1123305-80-5

477293-60-0

Step 2: Compound IV-8 (2.52 g, 7.99 mmol) was dissolved in tetrahydrofuran (13 mL). A 1 mol/L solution of tetrabutylammonium fluoride (15.97 mL, 15.97 mmol) was slowly added to this solution under cooling in an ice bath and the reaction mixture was continuously stirred at the same temperature for 10 hours. Upon completion of the reaction, water was added to the mixture and subsequently extracted with ethyl acetate. The organic layers were combined, washed sequentially with water and saturated saline, dried over anhydrous sodium sulfate and concentrated under reduced pressure to afford the target compound IV-4 (1.6 g, 99.5% yield). The product was characterized by 1H-NMR (CDCl3) with chemical shifts δ: 4.42-4.39 (1H, m), 4.02-3.99 (1H, m), 3.49-3.46 (2H, m), 2.11-2.08 (1H, m), 1.76-1.73 (1H, br m), 1.57-1.53 (1H, m), 1.47 (9H , s), 1.24 (3H, t, J = 5.26 Hz).