Yield:-

Reaction Conditions:

Stage #1: 4-benzyl-1-methyl-2-oxo-3-phenylpiperazinewith hydrogen;5%-palladium/activated carbon in acetic acid; under 5171.62 Torr;
Stage #2: with sodium hydroxide in water; pH=11 - 12;

Steps:

3 EXAMPLE 3; Preparation of 1-methyl-2-oxo-3-phenylpiperazine

4-Benzyl-1-methyl-2-oxo-3-phenylpiperazine (15 g, 0.535 moles) was dissolved in acetic acid (120 ml) and added 5% palladium-carbon (50% wet, 1.5 g). Reaction mass was hydrogenated at 100 psi. After completion of the reaction, reaction mixture was filtered and acetic acid was distilled under reduced pressure. Residue was dissolved in DM water (75 ml). pH was adjusted to 11.0-12.0 with 50% aqueous sodium hydroxide solution. The product was extracted with methylene chloride (2×75 ml) and washed with DM water (75 ml). The methylene chloride layer was concentrated under reduced pressure to obtain 10.1 g of 1-methyl-2-oxo-3-phenylpiperazine. [0032] 1H NMR (300 MHz) in CDCl3: δ(ppm); 1.99 (bs, 1H), 3.04 (s, 3H), 3.05-3.19 (m, 2H), 3.31-3.56 (m, 2H), 4.58 (s, 1H), 7.27-7.43 (m, 5H).

References:

US2004/242879,2004,A1 Location in patent:Page 3-4