To a solution of 100 (166 mg, 0.49 mmol) and 40 (0.06 mL, 0.473 mmol) in dichloroethane (4.9 mL) were sequentially added NaBH(OAc)3 (155 mg, 0.73 mmol) and HOAc (0.03 mL, 0.52 mmol). The reaction was stirred for 48 hours and then extracted with dichloromethane (2×30 mL). The dichloromethane extracts were washed with 2 N NaOH (aq. 15 mL), brine (15 mL), dried (MgSO4), and concentrated. The residue was chromatographed on silica gel (ethyl acetate) to give desired product as a yellow solid (51 mg, 23.7%).
