C1(C)C=CC(S(O[CH2:11][CH2:12][CH2:13][CH2:14][O:15][CH2:16][CH3:17])(=O)=O)=CC=1.[CH3:19][C@H:20]1[NH:25][CH2:24][CH2:23][N:22]([C:26]([O:28][C:29]([CH3:32])([CH3:31])[CH3:30])=[O:27])[CH2:21]1.C(N(CC)CC)C.C(=O)([O-])O.[Na+]>C(#N)C>[CH2:16]([O:15][CH2:14][CH2:13][CH2:12][CH2:11][N:25]1[CH2:24][CH2:23][N:22]([C:26]([O:28][C:29]([CH3:32])([CH3:31])[CH3:30])=[O:27])[CH2:21][C@H:20]1[CH3:19])[CH3:17]A mixture of 3 g of 4-ethoxybutyl p-toluenesulfonate, 2.65 g of tert-butyl (3R)-3-methylpiperazine-1-carboxylate, 3.07 mL of triethylamine, and 30 mL of acetonitrile was stirred at 90° C. for 3 hours. The reaction mixture was poured into a saturated aqueous sodium hydrogen carbonate solution, followed by extraction with ethyl acetate. The organic layer was washed with saturated brine and dried over anhydrous magnesium sulfate. The solvent was evaporated under reduced pressure and the residue was purified by silica gel column chromatography (chloroform/methanol) to obtain 3.1 g of tert-butyl (3R)-4-(4-ethoxybutyl)-3-methylpiperazine-1-carboxylate.
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