[CH2:1]([O:8][C:9]([N:11]1[CH2:16][CH2:15][NH:14][CH2:13][CH2:12]1)=[O:10])[C:2]1[CH:7]=[CH:6][CH:5]=[CH:4][CH:3]=1.[CH2:17]([O:19][C:20](=[O:25])[C:21](Br)([CH3:23])[CH3:22])[CH3:18].C(=O)([O-])[O-].[K+].[K+]>>[CH2:1]([O:8][C:9]([N:11]1[CH2:16][CH2:15][N:14]([C:21]([C:20]([O:19][CH2:17][CH3:18])=[O:25])([CH3:23])[CH3:22])[CH2:13][CH2:12]1)=[O:10])[C:2]1[CH:7]=[CH:6][CH:5]=[CH:4][CH:3]=1A mixture of piperazine-1-carboxylic acid benzyl ester (8.8 g, 40 mmol), 2-bromo-2-methylpropionic acid ethyl ester and potassium carbonate was stirred at 150° C. for 24 h. On cooling, the resulting mixture was partitioned between dichloromethane and water. The organic layer was washed with brine, dried (MgSO4) and evaporated under reduced pressure to give 4-(1-Ethoxycarbonyl-1-methyl-ethyl)-piperazine-1-carboxylic acid benzyl ester (10.2 g, 77%) as an oil.
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