Under nitrogen atmosphere, tetrahydrofuran (2 ml) was added to (2S)-5-benzyloxyimino-piperidine-2-carboxylic acid benzyl ester (0.168 g, 0.50 mmol), and the mixture was cooled down to −10° C. Sulfuric acid (0.302 g, 3.06 mmol) was added to the mixture, and then sodium borohydride (0.0567 g, 1.50 mmol) was added. After 22 hours of stirring, the reaction mixture was analyzed with high performance liquid chromatography to find that the mixture contained 0.136 g of the title compound, and the reduction reaction proceeded with the yield of 80%. The diastereo selectivity was (2S,5R)/(2S,5S)=80.4/19.6 (60.8% de).
