The general procedure for the synthesis of 2-piperazinone from ethyl chloroacetate and ethylenediamine was as follows: ethyl chloroacetate (4.9 g, 40 mmol) was dissolved in 40 mL of anhydrous ethanol and slowly added dropwise to 100 mL of ethylenediamine (24 g, 400 mmol) over 3.5 hours at room temperature. After the dropwise addition, the reaction mixture was allowed to stand for 2 hours. Subsequently, sodium ethoxide (15 mL, 40 mmol, 21% w/w denatured ethanol solution) was added, the precipitated sodium chloride was removed by filtration and the solvent was evaporated. To the resulting red oil 40 mL of DMF was added and stirred at room temperature for 24 h. The mixture was then heated at 60°C to 70°C while N2 gas was passed through to remove volatiles. The resulting yellow solid was separated by silica gel column chromatography, eluting using a solvent mixture (CHCl3:MeOH:NH4OH = 9:1:0.1) to give the crude product (3.3 g, 33 mmol, 82% yield). This yellow solid was used directly in the next step of the reaction without further purification. Pure white crystals were obtained by three times recrystallization from acetone.1H NMR (CDCl3): δ 1.70 (1H, br s), 3.03 (2H, t, J = 5.4 Hz), 3.37 (2H, td, J = 2.3, 5.4 Hz), 3.52 (2H, s), 6.54 (1H, br s).13C NMR (CDCl3): δ 42.31, 43.05, 49.83, 170.00. melting point: 132°C-134°C (uncorrected) [literature value: 136°C (corrected)] (American Chemical Society Journal, 62 (1940) 1202-1204).
