[C:1]([O:5][C:6]([N:8]1[CH2:13][CH:12]2[CH:10]([O:11]2)[CH2:9]1)=[O:7])([CH3:4])([CH3:3])[CH3:2].[FH:14].F.F.C(N(CC)CC)C.C([O-])([O-])=O.[Na+].[Na+]>>[C:1]([O:5][C:6]([N:8]1[CH2:13][C@@H:12]([OH:11])[C@H:10]([F:14])[CH2:9]1)=[O:7])([CH3:4])([CH3:3])[CH3:2]A mixture of 6-oxa-3-aza-bicyclo[3.1.0]hexane-3-carboxylic acid tert-butyl ester (5.4 mmol, from Example 316) and triethylamine trihydrofluoride (5.4 mmol) was heated at 90° C. for 2 h, then cooled to rt. Aq. Na2CO3 was added and the mixture was extracted with EtOAc. The organic phase was dried (Na2SO4), concentrated and purified by silica gel chromatography (0-40% EtOAc in heptane) to afford (trans)-3-fluoro-4-hydroxypyrrolidine-1-carboxylic acid tert-butyl ester as a colorless oil.
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