Cl[C:2]([O:4][CH2:5][CH:6]=[CH2:7])=[O:3].[N:8]1([C:20]([O:22][C:23]([CH3:26])([CH3:25])[CH3:24])=[O:21])[CH:12]([C:13]([O:15][C:16]([CH3:19])([CH3:18])[CH3:17])=[O:14])[CH2:11][CH2:10][NH:9]1.N1C=CC=CC=1>O1CCCC1>[N:9]1([C:2]([O:4][CH2:5][CH:6]=[CH2:7])=[O:3])[CH2:10][CH2:11][CH:12]([C:13]([O:15][C:16]([CH3:18])([CH3:19])[CH3:17])=[O:14])[N:8]1[C:20]([O:22][C:23]([CH3:26])([CH3:25])[CH3:24])=[O:21]Allyl chloroformate (0.488 ml, 4.59 mmol) was added dropwise to the solution of di-tert-butyl pyrazolidine-1,5-dicarboxylate (1 g, 3.67 mmol) and pyridine (0.371 ml, 4.59 mmol) in tetrahydrofuran (THF) (1.79 ml) at 0° C. The resulting solution was allowed to warm up to ambient temperature and stirred for 30 min. The reaction was filtered, and to the filtrate was added EtOAc. The solution was washed with brine. The organic layers were separated and dried over anhydrous Na2SO4. The crude product was purified by RP-HPLC to give 2,3-bis(1,1-dimethylethyl) 1-(2-propen-1-yl) 1,2,3-pyrazolidinetricarboxylate (749 mg, 2.101 mmol, 57% yield). MS (ES+) m/z 357.3 (MH+).
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