Triethylamine → 6-(2,4-Dichloro-benzylcarbamoyl)-2,6-diaza-spiro[3.3]heptane-2-carboxylic acid tert-butyl ester

To a stirred solution of 6-(tert-butoxycarbonyl)-2,6-diaza-spiro[3.3]heptane oxalate (200 mg, 1.01 mmol) in dichloromethane (10 mL) was added triethylamine (141 μl, 1.01 mmol) followed by 2,4-dichloro-1-(isocyanatomethyl)benzene (204 mg, 1.01 mmol). The reaction mixture was stirred at ambient temperature for 1 h. The crude reaction mixture was concentrated under reduced pressure. The residue was purified by chromatography (SiO2; methanol:dichloromethane 0:1 to 1:9) to give the title compound (344 mg, 85%) as a white solid.