[C:1]([O:5][C:6]([N:8]1[CH2:13][CH2:12][N:11]([C:14]([O:16][C:17]([CH3:20])([CH3:19])[CH3:18])=[O:15])[CH2:10][CH:9]1[C:21]([OH:23])=[O:22])=[O:7])([CH3:4])([CH3:3])[CH3:2].[C:24]([O-])([O-])=O.[Cs+].[Cs+].CI>C(#N)C>[N:8]1([C:6]([O:5][C:1]([CH3:4])([CH3:2])[CH3:3])=[O:7])[CH2:13][CH2:12][N:11]([C:14]([O:16][C:17]([CH3:20])([CH3:19])[CH3:18])=[O:15])[CH2:10][CH:9]1[C:21]([O:23][CH3:24])=[O:22]To a solution of 1,4-bis(tert-butoxycarbonyl)piperazine-2-carboxylic acid (2.5 g, 7.56 mol) in acetonitrile (25 mL) was Cs2CO3 (3.93 g, 12.06 mol) with stirring at RT. After 15 min, MeI (2.34 g, 16.48 mol) was added. The reaction mixture was stirred at rt for 14 h. The reaction was monitored by TLC. When SM was finished, reaction mixture was filtered through celite pad and filtrate was concentrated. Column chromatography of crude material afforded product 1,4-di-tert-butyl 2-methyl piperazine-1,2,4-tricarboxylate (29) as white solid (2.35 g, 90%).
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