[N:1]1([C:12]([O:14][C:15]([CH3:18])([CH3:17])[CH3:16])=[O:13])[CH2:6][CH2:5][CH2:4][C@H:3]([C:7](OCC)=[O:8])[CH2:2]1.O.[NH2:20][NH2:21]>CO.CCOC(C)=O>[NH:20]([C:7]([C@H:3]1[CH2:4][CH2:5][CH2:6][N:1]([C:12]([O:14][C:15]([CH3:18])([CH3:17])[CH3:16])=[O:13])[CH2:2]1)=[O:8])[NH2:21]To a solution of 6.28 g (24.4 mmol) of 1-(1,1-dimethylethyl) 3-ethyl (3S)-piperidine-1,3-dicarboxylate in 25 mL of MeOH was added 7.11 mL of hydrazine monohydrate (146 mmol, 5.98 eq.). The mixture was refluxed for 2 h and concentrated. The reaction could be monitored by LC/MS on a reversed-phase column at 220 nm wavelength. The crude material was taken up in EtOAc, and washed with 2×H2O, 1× sat. aqueous NaCl, and dried over Na2SO4. Filtration and concentration afforded 3.21 g of product (54.0% yield) as a viscous oil. The product was ca. 80% pure by hplc analysis and was used as such without further purification.
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