A solution of bis(2,2,2-trichloroethyl) 1,2-benzisoxazol-3-ylimidodicarbonate (3.00 g, 6.19 mmol), diisopropylethylamine (1.08 ml, 6.19 mmol) and 1-(tert-butoxycarbonyl)piperazine (2.30 g, 12.4 mmol) in dimethyl sulfoxide (20 ml) was stirred at 70° C. for 2 hours. The reaction mixture was poured to water and extracted with ethyl acetate. The extract was washed with water and dried over anhydrous magnesium sulfate, and the solvent was distilled off under reduced pressure. The residue was crystallized from hexane, which was purified by silica gel column chromatography (hexane:ethyl acetate=1:1), and then recrystallized from a mixed solvent of hexane and ethyl acetate to give 710 mg (33.2%) of the desired product.
