[NH:1]1[CH:5]([C:6]([O:8][C:9]([CH3:12])([CH3:11])[CH3:10])=[O:7])[CH2:4][CH:3]=[N:2]1.C([BH3-])#N.[Na+].[CH:17]1[CH:22]=[CH:21][C:20]([CH2:23][O:24][C:25](Cl)=[O:26])=[CH:19][CH:18]=1>C(O)(=O)C>[N:2]1([C:25]([O:24][CH2:23][C:20]2[CH:21]=[CH:22][CH:17]=[CH:18][CH:19]=2)=[O:26])[CH2:3][CH2:4][CH:5]([C:6]([O:8][C:9]([CH3:12])([CH3:11])[CH3:10])=[O:7])[NH:1]1To a solution of 1,1-dimethylethyl 4,5-dihydro-1H-pyrazole-5-carboxylate (5 g, 29.4 mmol) dissolved in acetic acid (75 mL) was added sodium cyanoborohydride (3.69 g, 58.8 mmol) over 10 minutes. After 30 min. the reaction mixture was concentrated. The intermediate was diluted with ethyl acetate and basified with sat. Na2CO3. The ethyl acetate was dried over sodium sulfate, filtered, and concentrated. The intermediate was diluted with tetrahydrofuran (THF) (75 mL), and triethylamine was added (8.19 mL, 58.8 mmol), followed by Cbz-Cl (2.1 mL, 14.69 mmol). After 2 h, the organic salts were filtered and the crude product was purified by silica gel column using 20-80% EtOAc/hexanes to afford 2.8 g (9.14 mmol) of 3-(1,1-dimethylethyl) 1-(phenylmethyl) 1,3-pyrazolidinedicarboxylate. LC-MS (ES) m/e 307.0 (M+H)+.
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