The reaction mixture was stirred at 0 °C for 4 hours. Following this time, the reaction was quenched with a saturated aqueous solution of NH4Cl (10 mL), and the mixture was transferred to a separatory funnel. The aqueous layer was extracted with CH2Cl2 (3 x 5 mL). The organic layers were collected, dried over Na2SO4, and concentrated under reduced pressure. The resulting residue was purified using a gradient of 0 to 5% EtOAc/hexanes on silica gel to yield 18 (colorless oil, 0.037 g, 0.048 mmol, 96% yield).