Tert-Butyl [(1R,2S,5S)-2-amino-5-[(dimethylamino)carbonyl]cyclohexyl]carbamate oxalate is prepared by the reaction of benzyl N-[(1S,2R,4S)-2-{[(tert-butoxy)carbonyl]amino}-4-(dimethylcarbamoyl)cyclohexyl]carbamate and Oxalic Acid. The steps are as follows:
Pd-C (230 mg) was added to a solution (35 mL) of benzyl t-butyl{(1S,2R,4S)-4-[(dimethylamino)carbonyl]cyclohexan-1,2-diyl}biscarbamate (2.3 g) in ethanol, and the mixture was stirred in a hydrogen atmosphere for 16 hours. Pd-C was removed by filtration, and the filtrate was concentrated under reduced pressure. Ethyl acetate (20 mL) and anhydrous oxalic acid (493.6 mg) were added to the residue, followed by stirring at room temperature for 17 hours. The formed crystals were recovered by filtration, to thereby yield 1.93 g of the Tert-Butyl [(1R,2S,5S)-2-amino-5-[(dimethylamino)carbonyl]cyclohexyl]carbamate oxalate.