[CH3:1][C:2]([CH3:9])([CH:7]=O)[C:3]([O:5][CH3:6])=[O:4].[N:10]1([C:16]([O:18][C:19]([CH3:22])([CH3:21])[CH3:20])=[O:17])[CH2:15][CH2:14][NH:13][CH2:12][CH2:11]1.C(O)(=O)C.C(O[BH-](OC(=O)C)OC(=O)C)(=O)C.[Na+]>C(Cl)Cl>[CH3:6][O:5][C:3](=[O:4])[C:2]([CH3:1])([CH3:9])[CH2:7][N:13]1[CH2:12][CH2:11][N:10]([C:16]([O:18][C:19]([CH3:22])([CH3:21])[CH3:20])=[O:17])[CH2:15][CH2:14]1Stir a solution of methyl 2,2-dimethyl-3-oxo-propanoate (30.88 g, 237.31 mmoles) and tert-butyl piperazine-1-carboxylate (34.00 g, 182.55 mmoles) in DCM (500 mL) at room temperature for 20 minutes. Add acetic acid (2 equiv); 20.92 mL, 365.09 mmoles) followed by sodium triacetoxyborohydride (1.4 equiv; 54.17 g, 255.56 mmoles) over 0.5 h and stir the resulting mixture stirred at room temperature overnight. Carefully quench with water (250 mL) and transfer the mixture to a separating funnel with DCM (300 mL). Wash the resulting organic layer with brine. Dry over MgSO4, filter and evaporate to give tert-butyl 4-(3-methoxy-2,2-dimethyl-3-oxopropyl)piperazine-1-carboxylate. (58 g, 100%). MS (m/z): 301.2 (M+1).
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