[C:1]([O:5][C:6]([N:8]1[CH2:13][CH2:12][NH:11][CH2:10][CH2:9]1)=[O:7])([CH3:4])([CH3:3])[CH3:2].[CH2:14]=[C:15]1[O:19][C:17](=[O:18])[CH2:16]1>CN(C=O)C>[C:17]([N:11]1[CH2:12][CH2:13][N:8]([C:6]([O:5][C:1]([CH3:4])([CH3:2])[CH3:3])=[O:7])[CH2:9][CH2:10]1)(=[O:18])[CH2:16][C:15]([CH3:14])=[O:19]1-tert-Butoxycarbonylpiperazine (103 g) was dissolved in DMF (600 mL) and diketene (56 mL) was added over 20 min at room temperature. The mixture was stirred for 2 hr. The solvent was evaporated under reduced pressure and the residue was diluted with ethyl acetate. The mixture washed with water and saturated brine and dried. The solvent was evaporated under reduced pressure to give 1-acetoacetyl-4-tert-butoxycarbonyl piperazine (129 g) as a pale-brown powder.
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