To a solution of 1-tert-butyl piperazine-1,3-dicarboxylate (4.5 g, 19.565 mmol, 1.0 eq.) in dichloromethane (DCM, 125 mL) were sequentially added triethylamine (TEA, 5.93 g, 58.70 mmol, 3.0 eq.) and benzyl chloroformate (CbzCl, 5 g, 29.35 mmol, 3.0 eq.). The reaction mixture was stirred at room temperature for 4 h, during which the reaction progress was monitored by liquid chromatography-mass spectrometry (LC-MS) and thin layer chromatography (TLC). Upon completion of the reaction, the mixture was concentrated and the resulting residue was purified by silica gel column chromatography (eluent ratio: petroleum ether/ethyl acetate = 5/1) to afford the target product (S)-1-((benzyloxy)carbonyl)-4-(tert-butoxycarbonyl)piperazine-2-carboxylic acid (5 g, 70% yield) as a white solid.
