A mixture of 1′-(3-Methoxy-4-nitro-phenyl)-[4,4′]bipiperidinyl-1-carboxylic acid tert-butyl ester (2.0 g, 4.77 mmol), iron powder (1.33 g, 23.85 mmol), 1N hydrogen chloride (9.54 mL, 9.54 mmol) in ethanol (50 mL) is stirred at 80° C. for 3 h. After cooling to room temperature, 2N hydrogen chloride (5 mL) and ethyl acetate are added and then the mixture is filtrated. After concentration in vacuo, the mixture is extracted with AcOEt, washed with brine, dried over sodium sulfate and evaporated to give 1′-(4-Amino-3-methoxy-phenyl)-[4,4′]bipiperidinyl-1-carboxylic acid tert-butyl ester (1.77 g, 95% yield) as pale purple solids.
