The compound (500 mg) prepared in Step 1, N-Boc-piperazine (500 mg) and tassium carbonate (2.0 g) were dissolved in dimethylformamide (3 ml), and stirred at 90° C. for 2 hours. The dimethylformamide of the mixed solution was removed by distillation under reduced pressure, and extracted with ethyl acetate. The extracted organic layer was washed with saturated brine, and water was removed with sodium sulfate, and the solvent was removed by distillation under reduced pressure. The solvent-removed mixture was purified by column chromatography to obtain a yellow target compound.
