[O:1]=[C:2]1[NH:7][CH2:6][CH2:5][N:4]([C:8]([O:10][C:11]([CH3:14])([CH3:13])[CH3:12])=[O:9])[CH2:3]1.[CH3:15][N:16]1[CH:20]=[C:19](I)[CH:18]=[N:17]1.C(O)CO.P([O-])([O-])([O-])=O.[K+].[K+].[K+]>C(O)(C)C.[Cu](I)I>[CH3:15][N:16]1[CH:20]=[C:19]([N:7]2[CH2:6][CH2:5][N:4]([C:8]([O:10][C:11]([CH3:14])([CH3:13])[CH3:12])=[O:9])[CH2:3][C:2]2=[O:1])[CH:18]=[N:17]1To a solution of tert-butyl 3-oxopiperazine-1-carboxylate (0.164 g, 0.819 mmol) in 3 mL of isopropanol under an atmosphere of nitrogen was added 1-methyl-4-iodo-1H-pyrazole (0.204 g, 0.983 mmol), ethylene glycol (0.051 g, 0.82 mmol), copper iodide (0.031 g, 0.16 mmol), and potassium phosphate (0.695 g, 3.28 mmol). The reaction was heated to 100° C. for 8 h, cooled to rt, and concentrated in vacuo. The residue was dissolved in dichloromethane, washed with water, dried over sodium sulfate, filtered, and concentrated in vacuo. The residue was purified via silica gel chromatography, eluting with 10-100% ethyl acetate in hexanes to provide tert-butyl 4-(1-methyl-1H-pyrazol-4-yl)-3-oxopiperazine-1-carboxylate that gave a mass ion (ES+) of 281.1 for [M+H]+.
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