Methyl trans-4-aminocyclohexanecarboxylate (132 g, 401 mmol) was suspended in dichloromethane (1000 ml) under cooling conditions in an ice bath. Triethylamine (123 ml, 882 mmol) and di-tert-butyl dicarbonate (Boc2O, 101 ml, 440 mmol) were sequentially added to the suspension and the reaction was stirred for 10 minutes. Subsequently, the reaction mixture was transferred to room temperature and continued stirring for 2 hours. After completion of the reaction, the solvent was removed by rotary evaporator under reduced pressure. The residue was dissolved in aqueous citric acid solution (prepared by dissolving 50 g of citric acid monohydrate in 400 ml of water, pH adjusted to 4) and extracted with ethyl acetate. The organic phase was sequentially washed with water and dried with anhydrous magnesium sulfate. Finally, the organic phase was concentrated under reduced pressure to quantitatively obtain the target product methyl trans-4-(tert-butoxycarbonylamino)cyclohexanecarboxylate. The product was characterized by 1H-NMR (DMSO-d6) with the following chemical shift δ (ppm): 1.06-1.25 (m, 2H), 1.25-1.43 (m, 2H), 1.37 (s, 9H), 1.75-1.94 (m, 4H), 2.19 (tt, 1H, J = 11.7,3.9 Hz), 3.07-3.24 (m. 1H), 3.58 (s, 3H), 6.74 (d, 1H, J = 6.6 Hz).
