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To a solution of 24E (0.1 g, 0.124 mmol) in acetonitrile (5 mL) and dichloromethane (2.5 mL) at 0° C., was added phosgene solution (20% in toluene, 0.072 mL, 0.136 mmol) dropwise. The mixture was stirred at 0° C. for 30 min. Extra phosgene was removed by bubbling Ar for 20 min. The crude was then added dropwise via syringe pump into a solution of TEA (0.138 mL, 0.993 mmol) in dichloromethane (60 mL) at rt over 3.0 h. The solution was stirred at rt over night. Solvent was removed, and the crude product was purified by flash chromatography (0-80% EtOAc/hexanes) to give a mixture of diastereoisomers (0.1 g, 0.120 mmol, 97% yield). The diastereomers were separated by a prep chiral HPLC (R,R-Whelk-O column 21.1×250 mm) to give 24F (38 mg, 76% yield). MS (ESI) (m/z): 831.9 (M+H)+.

1. customExtra phosgene was removed
2. customby bubbling Ar for 20 min
3. stirringThe solution was stirred at rt over night
4. customSolvent was removed
5. customthe crude product was purified by flash chromatography (0-80% EtOAc/hexanes)
6. customto give
7. additiona mixture of diastereoisomers (0.1 g, 0.120 mmol, 97% yield)
8. customThe diastereomers were separated by a prep chiral HPLC (R,R-Whelk-O column 21.1×250 mm)