136 mg (0.46 mmol) of triphosgene are added to 10 ml of dichloro-methane. The medium is cooled to 0° C. and a solution of 580 mg (1.37 mmol) of N-(2,6-diisopropylphenyl)-2-[(1-phenylaminocyclohexyl-methyl)amino]acetamide and 260 μl (1.49 mmol) of diisopropylethylamine in 10 ml of dichloromethane are added drop by drop. The mixture is allowed to rise to room temperature and is stirred for one night. The medium is then poured into water and extracted with dichloromethane. The organic phases are collected and washed with water. They are dried over sodium sulfate. The solvents are evaporated. The residue is chromatographed on silica gel (heptane/ethyl acetate 80/20) and 485 mg of N-(2,6-diisopropylphenyl)-2-(2-oxo-1-phenyl-1,3-diazaspiro[4.5]dec-3-yl)acetamide are obtained in the form of a white solid after having been precipitated in dichloromethane and heptane, filtered and dried. M.p. 107-9° C., yield=79%.
