S(=O)(=O)(O)O.[BH4-].[Na+].[CH2:8]([O:15][C:16]([C@@H:18]1[CH2:23][CH2:22][C:21](=[N:24][O:25][CH2:26][C:27]2[CH:32]=[CH:31][CH:30]=[CH:29][CH:28]=2)[CH2:20][NH:19]1)=[O:17])[C:9]1[CH:14]=[CH:13][CH:12]=[CH:11][CH:10]=1.C12(CS(O)(=O)=O)C(C)(C)C(CC1)CC2=O>O1CCCC1>[CH2:8]([O:15][C:16]([C@@H:18]1[CH2:23][CH2:22][C@@H:21]([NH:24][O:25][CH2:26][C:27]2[CH:32]=[CH:31][CH:30]=[CH:29][CH:28]=2)[CH2:20][NH:19]1)=[O:17])[C:9]1[CH:10]=[CH:11][CH:12]=[CH:13][CH:14]=1Under nitrogen atmosphere, tetrahydrofuran (3 ml) and sulfuric acid (0.151 g, 1.53 mmol) were added to sodium borohydride (0.101 g, 2.66 mmol). The obtained mixture was added dropwise at −10° C. to the mixture consisting of (2S)-5-benzyloxyimino-piperidine-2-carboxylic acid benzyl ester (0.168 g, 0.50 mmol), (+)-camphorsulfonic acid (0.695 g, 2.99 mmol) and tetrahydrofuran (2 ml) for 0.5 hour. After 22 hours of stirring, the obtained reaction mixture was analyzed with high performance liquid chromatography to find that the reaction mixture contained 0.125 g of the title compound, and the reduction reaction proceeded with yield of 74%. The diastereo selectivity was (2S,5R)/(2S,5S)=81.4/18.6 (62.8% de).
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