Cl.[CH3:2][O:3][C:4]([C@H:6]1[CH2:11][CH2:10][C@H:9]([NH2:12])[CH2:8][CH2:7]1)=[O:5].[O-]S([O-])(=O)=O.[Mg+2].[CH:19](=O)[C:20]1[CH:25]=[CH:24][CH:23]=[CH:22][CH:21]=1.[BH4-].[Na+]>CO.O>[CH3:2][O:3][C:4]([CH:6]1[CH2:11][CH2:10][CH:9]([NH:12][CH2:19][C:20]2[CH:25]=[CH:24][CH:23]=[CH:22][CH:21]=2)[CH2:8][CH2:7]1)=[O:5]To a solution of trans-4-amino-cyclohexylcarboxylic acid methyl ester hydrochloride (4.5 g, 23.24 mmol) in MeOH (30 mL) is added TEA (1.3 mL, 9.339 mmol), MgSO4 (4.2 g, 34.88 mmol), and benzaldehyde (2.5 mL, 24.74 mmol). The mixture stirs 1 h. The mixture is then cooled to 0° C. and NaBH4 (5.0 g, 132.2 mmol) is added portionwise over 0.5 h. The mixture stirs 1 h at ambient temperature. Then H2O (200 mL) is added and the mixture is extracted with EtOAc (2×500 mL), dried and concentrated. The resulting solid is purified by flash chromatography (gradient elution: 0-100% EtOAc/Hep) which affords 2.7 g of 4-benzylamino-cyclohexanecarboxylic acid methyl ester. LC/MS: [M+H]+ 248, Rt=0.82 min (method 11).
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