After the reaction was complete, the reaction mixture was cooled, poured into saturated aq NH4Cl (10 mL) and extracted with hexanes (3 × 6 mL). Combined organic extracts was washed with water (2 × 10 mL), brine (2 × 10 mL), dried over Na2SO4 and evaporated under reduced pressure. The crude residue was purified by flash column chromatography using gradient EtOAchexane as eluent.