The mixture was transferred to a separatory funnel and further diluted with water (100 mL). The aqueous layer was extracted with EtOAc (2 x 100 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 10% EtOAc/hexanes on silica gel to yield 4. Over two batches: (colorless oil, 5.7 g, 18.1 mmol, 54% yield) and recovered starting material: 3 g (25%).