[H-].[Na+].[CH2:3]([N:10]1[CH2:15][CH2:14][NH:13][C:12](=[O:16])[CH:11]1[C:17]1[CH:22]=[CH:21][CH:20]=[CH:19][CH:18]=1)[C:4]1[CH:9]=[CH:8][CH:7]=[CH:6][CH:5]=1.[CH3:23]I>CN(C)C=O.O>[CH2:3]([N:10]1[CH2:15][CH2:14][N:13]([CH3:23])[C:12](=[O:16])[CH:11]1[C:17]1[CH:22]=[CH:21][CH:20]=[CH:19][CH:18]=1)[C:4]1[CH:5]=[CH:6][CH:7]=[CH:8][CH:9]=115.3 g of sodium hydride (65% dispersion in mineral oil, 0.414 moles) was suspended in 250 ml of N,N-dimethylformamide at 10° C. To this suspension, 100 g of 4-benzyl-2-oxo-3-phenylpiperazine (0.376 moles) was added portionwise over a period of 30 min and stirred for 15 min. A solution of 64 g of methyl iodide (0.45 moles) in 50 ml of N,N-dimethylformamide was added slowly in 45 min maintaining the temperature below 25° C. and maintained for 1 hour. After completion of the reaction, mass was poured slowly in 1000 ml of cold water (15° C.). The product was extracted with toluene (1×500 ml, 1×300 ml) from aqueous phase. Toluene layer was washed with water (2×200 ml) and concentrated. To the residue, 250 ml of cyclohexane was added and cooled to 10° C. with stirring. Filtered the product and washed with precooled cyclohexane to obtain 98.5 g of 4-benzyl-1-methyl-2-oxo-3-phenylpiperazine product (yield: 93.8%, purity: 99.15 by HPLC)
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