Step A: Preparation of methyl trans-4-aminocyclohexanecarboxylate hydrochloride. Trans-4-aminocyclohexanecarboxylic acid (200 mg, 1.40 mmol) was suspended in methanol (5.5 mL) and cooled to -10 °C. Thionyl chloride (204 μL, 2.79 mmol) was added dropwise under stirring and the reaction mixture was stirred at -10 °C for 15 min. Subsequently, the reaction system was slowly warmed to room temperature and stirring was continued for 15 min, after which it was heated to reflux for 1 hr. After completion of the reaction, the reaction was cooled to room temperature and the reaction mixture was concentrated under reduced pressure to afford the white solid product methyl trans-4-aminocyclohexanecarboxylate hydrochloride (260 mg, 96.1% yield). Mass spectral analysis (APCI) showed m/z = 158.0 ([M+H]+).
