The aqueous layer was extracted with CH2Cl2 (3 x 15 mL). The organic layer was collected, dried over Na2SO4, and concentrated under reduced pressure. The resulting residue was purified using a gradient of 0 to 15% EtOAc/hexanes on silica gel to yield compound 11 (colorless oil, 0.937 g, 2.38 mmol, 81% yield). A 100 mL round-bottom flask was charged with a stir bar, 11 (920 mg, 2.33 mmol, 1 equiv.), and CH2Cl2 (25 mL). The reaction flask was cooled to 0 °C using an ice-water bath. Sequentially, TMEDA (0.7 mL, 0.55 g, 4.7 mmol, 2 equiv.) and CbzCl (1.0 mL, 1.2 g, 7.03 mmol, 3 equiv.) were added dropwise. The reaction mixture was warmed to room temperature over a period of 40 hours. Subsequently, the reaction was quenched with a saturated aqueous solution of NH4Cl (20 mL), and the mixture was transferred to a separatory funnel. The aqueous layer was extracted with CH2Cl2 (2 x 30 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 20% EtOAc/hexanes on silica gel to yield 12 (colorless oil, 860 mg, 1.63 mmol, 70% yield).