[F:1][C:2]1[CH:3]=[C:4]([CH:6]=[C:7]([F:9])[CH:8]=1)[NH2:5].[CH3:10][C:11]1([CH3:20])[O:15][C@H:14]([CH2:16][CH:17]=O)[C:13](=[O:19])[O:12]1.C(O)(=O)C.[BH4-].[Na+]>ClCCCl>[F:1][C:2]1[CH:3]=[C:4]([NH:5][CH2:17][CH2:16][C@H:14]2[O:15][C:11]([CH3:20])([CH3:10])[O:12][C:13]2=[O:19])[CH:6]=[C:7]([F:9])[CH:8]=1
To a stirred solution of 3,5-difluoroaniline (4.0 g, 31.0 mmol), (R)-2-(2,2-dimethyl-5-oxo-1,3-dioxolan-4-yl)acetaldehyde (4.9 g, 31.0 mmol) and acetic acid (1.7 ml, 31.0 mmol) in 1,2-dichloroethane (100 mL) under nitrogen at 0° C. was added sodium borohydride (1.17 g, 31.0 mmol mol) in portions over 10 minutes. The resulting mixture was stirred at RT for 2.5 hours. After cooling to 0° C. the reaction mixture was quenched by the careful addition of saturated aqueous NaHCO3 (100 mL) followed by DCM (100 mL). The phases were separated and the aqueous phase was extracted with dichloromethane (2×100 mL). The combined organic extracts were dried over MgSO4 and concentrated under reduced pressure to provide the crude (R)-5-[2-(3,5-difluorophenylamino)ethyl]-2,2-dimethyl-1,3-dioxolan-4-one as a yellow oil (8.07 g, 29.7 mmol, 96% yield) which was used without any further purification in the next reaction step. LC/MS (10%-99% CH3CN (0.035% TFA)/H2O (0.05% TFA), m/z: M+1 obs=272.3; tR=1.76 min.
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