Yield: 0.81 mg (63%); mp 112-114 °C; Rf = 0.37 (CH2Cl2/MeOH 9:1); was added dropwise to the solution. After 1 h, the ice bath was removed and the mixture was allowed to warm up to room temperature overnight. Then, the solution was cooled to 0 °C and quenched with saturated NH4Cl (20 mL). The mixture was diluted with Et2O, the phases were separated and the organic phase was dried over Na2SO4, filtered and concentrated under vacuum. The crude product was purified by column chromatography (EtOAc/n-hexanes 1:1) to obtain a yellow oil. Yield: 2.25 g (96%); Rf = 0.50 (EtOAc/n-hexanes 1:2); was added and the phases were separated. The organic phase was washed with 10% citric acid (50 mL), saturated NaHCO3 (50 mL), brine (50 mL), dried over Na2SO4, filtered and concentrated under vacuum. The product was used in the next step without further purification.