1353893-22-7

365998-36-3

144-62-7

1353893-22-7

General synthesis of tert-butyl ((1R,2S,5S)-2-amino-5-(dimethylcarbamoyl)cyclohexyl)carbamate oxalate hydrate of ((1R,2S,5S)-2-amino-5-(dimethylcarbamoyl)cyclohexyl)carbamate from ((1R,2S,5S)-2-amino-5-(dimethylcarbamoyl)cyclohexyl)carbamate as raw materials (45.61g, 0.16mol) and oxalic acid (18.87g, 0.21mol) The procedure was as follows: acetonitrile (595 ml) and water (43 ml) were added to tert-butyl ((1R,2S,5S)-2-amino-5-(dimethylcarbamoyl)cyclohexyl)carbamate, and the mixture was heated with stirring until the internal temperature was maintained at 50-70 °C. A pre-prepared solution consisting of anhydrous oxalic acid and acetonitrile (255 ml) was added dropwise to the solution over a period of 1 hour while maintaining the internal temperature at 50-70 °C. After completion of the dropwise addition, the reaction mixture was continued to be stirred at 50-70 °C for 5 hours and subsequently cooled to an internal temperature of 20-40 °C. The precipitated crystals were collected by filtration, washed with acetonitrile and dried to give monohydrate crystals of the target compound (59.14 g, 94.1% yield). The powder X-ray diffraction pattern of the resulting monohydrate crystals was consistent with formula (1b), and the results of their thermal analysis were consistent with those of the Type 2 monohydrate crystals in Example 2, as shown in FIGS. 4 and 8.