[C:1]([O:5][C:6]([N:8]1[CH2:12][CH2:11][C@H:10]([NH2:13])[CH2:9]1)=[O:7])([CH3:4])([CH3:3])[CH3:2].[Cl:14][C:15]1[CH:22]=[C:21]([Cl:23])[CH:20]=[CH:19][C:16]=1[CH:17]=O.[BH4-].[Na+]>CO>[C:1]([O:5][C:6]([N:8]1[CH2:12][CH2:11][C@H:10]([NH:13][CH2:17][C:16]2[CH:19]=[CH:20][C:21]([Cl:23])=[CH:22][C:15]=2[Cl:14])[CH2:9]1)=[O:7])([CH3:4])([CH3:2])[CH3:3]Stir a mixture of (S)-3-amino-pyrrolidine-1-carboxylic acid tert-butyl ester (15.07 g, 81.0 mmol) and 2,4-dichlorobenzaldehyde (13.46 g, 76.9 mmol) in dry methanol (250 mL) at room temperature under nitrogen overnight. Add slowly sodium borohydride (4.74 g, 125.4 mmol) and stir for 10 min. Concentrate and add 2 N NaOH (150 mL) and extract with diethyl ether. Combine the organic layers, wash with saturated aqueous sodium chloride, dry (magnesium sulfate) and concentrate to give (S)-3-(2,4-dichlorobenzylamino)-pyrrolidine-1-carboxylic acid tert-butyl ester which may be used without further purification (26.9 g, 100%).
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