Cl.Cl.[NH:3]1[CH2:8][CH2:7][NH:6][CH2:5][CH:4]1[C:9]([OH:11])=[O:10].[C:12](=O)(O)[O-].[Na+].C[Si](C=[N+]=[N-])(C)C>CO.C(Cl)Cl>[NH:3]1[CH2:8][CH2:7][NH:6][CH2:5][CH:4]1[C:9]([O:11][CH3:12])=[O:10]piperazine-2-carboxylic acid dihydrochloride (750 mg, 3.7 mmol) was suspended in MeOH (15 mL) and sodium bicarbonate (620 mg, 7.4 mmol) was added and stirred for 4 h. The reaction mixture was diluted with CH2Cl2 (15 mL) and cooled to 0° C. (Trimethylsilyl)diazomethane (15 mL, 2M in hexane) was added dropwise until the yellow color persisted. The solution was stirred at room temperature for 3 h and concentrated under reduced pressure. The crude product was purified by column chromatography (neutral alumina, eluent 5-6% MeOH in CHCl3) to get methyl piperazine-2-carboxylate (150 g, yield 28%). 1H NMR (300 MHz, CDCl3) δ 3.74 (s, 3H), 3.51-3.47 (dd, J=8.0 Hz, 3.4 Hz, 1H), 3.24-3.19 (dd, J=12.1 Hz, 3.3 Hz, 1H), 3.04-2.99 (m, 1H), 2.96-2.86 (m, 3H), 2.83-2.77 (m, 1H)
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