To a solution of 73 (102 mg, 0.301 mmol) in dichloroethane (3.0 mL) under N2 was added 40 (0.04 mL, 0.315 mmol). The reaction was stirred for 24 minutes before the sequential addition of NaBH(OAc)3 (94 mg, 0.444 mmol) and AcOH (0.02 mL, 0.349 mmol). The reaction was stirred for 19 hours and then extracted with ethyl acetate (2×30 mL). The ethyl acetate extracts were washed with 2 N NaOH (aq. 15 mL), brine (15 mL), dried (MgSO4), and concentrated. The residue was chromatographed on silica gel (dichloromethane to 30:1 to 20:1 dichloromethane/methanol) to give the desired product as a yellow solid (75 mg, 55%).
