Diisopropylethylamine → (3R)-3-methyltetrahydro-2H-pyrazino[1,2-a]pyrazine-1,4(3H,6H)-dione

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To a solution of N,N′-diboc-piperazine-2-carboxylic acid (2 g, 6.06 mmol) in 50 mL of dichloromethane and was added TBTU (2.138 g, 6.66 mmol) and diisopropylethyl amine (1.3 mL, 7.26 mmol). The reaction was stirred for 45 min. In the meantime, a suspension of D-alanine methyl ester hydrochloride (1.249 g, 12.11 mmol) and diisopropylethylamine (3.27 mL, 18.76 mmol) in 20 mL of dichloromethane and 5 mL of DMF was stirred and finally added to the reaction mixture. The reaction was left stirring at room temperature overnight. UPLC-MS analysis showed the expected product (peak at 0.72 min, m/z=416 (M+1), 360 (M−t-Bu+1). The reaction was diluted with dichloromethane and extracted with sat. NaHCO3, dried (Na2SO4), and the solvent removed. The crude (4.242 g) was taken to the next step without further purification.

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