Benzyl Bromide → 4-(1-benzyl-2-oxo-1,4-dihydro-2H-benzo[d][1,3]oxazin-5-yl)-piperazine-1-carboxylic acid tert-butyl ester

To a solution of 4-(2-oxo-1,4-dihydro-2H-benzo[d][1,3]oxazin-5-yl)-piperazine-1-carboxylic acid tert-butyl ester (43 m g, 0.13 mmol) in 2 ml anhydrous dimethylformanide was added sodium hydride (8 mg of a 60% suspension in mineral oil, 0.2 mmol) portion-wise at 0° C. The solution was stirred with a magnetic stirrer at 0° C. for 20 minutes, at which time the initial off-gassing ended. Benzyl bromide (0.02 ml, 0.17 mmol) was added in one portion and the reaction mixture was stirred at 0° C. for an hour. The solution was allowed to warm to room temperature and the reaction mixture was partitioned between water and ethyl acetate. The aqueous layer was extracted with ethyl acetate and the combined organic fractions were washed with water and brine. After drying over MgSO4, the organic fraction was concentrated in vacuo and resulting brown residue was purified by prep TLC to give 33 mg of 4-(1-benzyl-2-oxo-1,4-dihydro-2H-benzo[d] [1,3]oxazin-5-yl)-piperazine-1-carboxylic acid tert-butyl ester as a white solid (60%). MS: 424 (M+H)+.