2,4-dinitrobenzene (1.2 g), N-Boc-piperazine (1.4 g) and potassium carbonate (1.2 g) were dissolved in dimethylformamide (5 mL) and stirred at 50° C. overnight. Then, the mixture was distilled under reduced pressure to remove dimethylformamide, added with water, and extracted with ethyl acetate. The thus obtained organic layer was washed with brine, and water was removed with sodium sulfate, and the solvent was removed by distillation under reduced pressure. The mixture was purified by column chromatography (silica gel) to obtain target compounds (Rf=0.3, hexane:ethyl acetate=2:1) and (tert-butyl-4-(5-fluoro-2-nitrophenyl)piperazin-1-carboxylate (Rf=0.6, hexane:ethyl acetate=2:1).
