To a solution of 21A (310 mg, 1.096 mmol) in 1,2-dichloroethane (7 mL) was added benzaldehyde (235 mg, 2.193 mmol), followed by sodium triacetoxyboro-hydride (650 mg, 3.069 mmol) and AcOH (200 mg, 3.29 mmol). The reaction mixture was stirred at RT for 4 h, then diluted with EtOAc, washed with saturated aqueous NaHCO3, water, brine, dried (Na2SO4) and concentrated. The resulting residue was chromatographed (silica gel) eluting with EtOAc/hexane 1:5 to give the title compound as light yellow foam (325 mg, 80%).
