Synthesis
Step 1: Synthesis of tert-butyl 4-benzyl-3-oxopiperazine-1-carboxylate
Sodium hydride (60% in mineral oil, 18.11 g, 452 mmol) was mixed with 35 mL of hexane, ground and dried under nitrogen protection and subsequently suspended in 1500 mL of tetrahydrofuran. To this suspension, 1-Boc-3-piperazinone (75.057 g, 200.4 mmol) was added in batches at 0 °C and the addition process lasted for 15 min. After 90 minutes of reaction, benzyl bromide (71.01 g, 415.1 mmol) was added and then the reaction mixture was gradually warmed up to room temperature and stirred for 18 hours. Upon completion of the reaction, the reaction was quenched with deionized water and extracted with ether. The combined organic layers were washed sequentially with water and brine and dried over anhydrous magnesium sulfate. The solvent was removed by concentration under reduced pressure to give the crude product, which was purified by recrystallization from hexane to give tert-butyl 4-benzyl-3-oxopiperazine-1-carboxylate (83.5 g, 76% yield) as a white crystalline solid.
References
[1] Patent: US2009/209553, 2009, A1. Location in patent: Page/Page column 14-15
[2] Tetrahedron Letters, 1996, vol. 37, # 41, p. 7339 - 7342
[3] Synthesis, 2005, # 3, p. 465 - 469
[4] Patent: US2004/259884, 2004, A1. Location in patent: Page 13
[5] Bioorganic and Medicinal Chemistry, 2008, vol. 16, # 3, p. 1431 - 1443
