Dissolve (S)-3-(cyanomethyl)piperazine-1-carboxylic acid tert-butyl ester (2.25g, 10mmol) in 15mL dichloromethane, add N,N-diisopropylethylamine at room temperature (3.87g, 30mmol) was cooled to 0°C, benzyl chloroformate was added dropwise, and reacted at low temperature for 2h. Add 25 mL of water to the reaction solution, extract the aqueous phase with dichloromethane (30 mL×3), combine the organic phases, wash the organic phase with water (20 mL×2), dry with anhydrous sodium sulfate, concentrate, and separate and purify the crude product by silica gel column chromatography (Ethyl acetate/petroleum ether (v/v)=1:20-1:5) to obtain 1-Benzyl 4-(tert-butyl) (S)-2-(cyanomethyl)piperazine-1,4-dicarboxylate (3.1 g, yield: 86%).
