Step 4: To a solution of tert-butyl (cis-4-azido-cyclohexyl)-carbamate (6.3 g, 26 mmol) in methanol (100 mL) was added 5% Pd/C (Degussa type, 0.63 g) under argon protection. The reaction flask was sealed, evacuated and backfilled with hydrogen, and the process was repeated three times. The reaction mixture was stirred for 2 h at room temperature under an atmosphere of hydrogen at 1 atm. Upon completion of the reaction, the catalyst was removed by filtration through a diatomaceous earth pad and the filtrate was concentrated under reduced pressure. The residue was partitioned between ether (Et2O) and 1N hydrochloric acid (HCl) solution. The aqueous phase was separated and alkalized with sodium hydroxide solution to pH > 10, followed by extraction with ethyl acetate (EtOAc, 2 × 100 mL). The organic phases were combined, washed with saturated sodium chloride solution (brine), dried over anhydrous sodium sulfate (Na2SO4), filtered and concentrated under reduced pressure to afford the white solid product (tert-butyl cis-4-amino-cyclohexyl)-carbamate (3.6 g, 64% yield). Mass spectrometry (MS) analysis showed (M+H)+ = 215.6.
