Triethylamine (169 mL) was added at 60° C. to a suspension (550 mL) of t-butyl {(1R,2S,5S)-2-amino-5-[(dimethylamino)carbonyl]cyclohexyl}carbamate oxalate (100.1 g) in acetonitrile. At the same temperature, ethyl[5-chloropyridin-2-yl]amino](oxo)acetate hydrochloride (84.2 g) was added to the mixture, followed by stirring for 6 hours. Thereafter, the mixture was stirred at room temperature for 16 hours. Water was added to the reaction mixture, followed by stirring at 10° C. for 1.5 hours. The formed crystals were recovered by filtration, to thereby yield 106.6 g of the title compound.
