Reaction SMILES: C(O)(=O)C(C)C.[BH4-].[Na+].[C:9]1([C@@H:15]([NH:17][C:18]2[CH2:23][CH2:22][CH2:21][CH2:20][C:19]=2[C:24]([O:26][CH2:27][CH3:28])=[O:25])[CH3:16])[CH:14]=[CH:13][CH:12]=[CH:11][CH:10]=1>C1(C)C=CC=CC=1>[C:9]1([C@@H:15]([NH:17][C@H:18]2[CH2:23][CH2:22][CH2:21][CH2:20][C@H:19]2[C:24]([O:26][CH2:27][CH3:28])=[O:25])[CH3:16])[CH:10]=[CH:11][CH:12]=[CH:13][CH:14]=1
Reactant: CCOC(=O)C1=C(N[C@@H](C)c2ccccc2)CCCC1
Agent: [BH4-]
Agent: [Na+]
Solvent: Cc1ccccc1
Solvent: CC(C)C(=O)O
Product: CCOC(=O)[C@@H]1CCCC[C@@H]1N[C@@H](C)c1ccccc1
Temperature: 3.5 °C
Yield: 108.2 %

Procedure:
Isobutyric acid (1.86 L, 1.762 Kg, 20.0 mol, 20.0 equiv.) was added to a 4 L reactor under nitrogen and cooled to 2-5° C. temperature. Sodium borohydride (113.49 g, 3.0 mol, 3.0 mole equiv.) is added with agitation between 0-10° C. in NLT 2 h. The mixture warmed to 18° C. temperature and mixed for an additional NLT 15 min. The solution was cooled to −5° C. to −8° C. then the toluene solution containing the (S)-ethyl 2-(1-phenylethylamino)cyclohex-1-enecarboxylate (8, 273.37 g, 1.0 mol, 1.0 equiv.) was added over 50 min while maintaining the temperature at 0±2° C. The contents were mixed for 2 h and 40 min and quenched by the slow addition of 1 L of 4N hydrochloric acid while maintaining the temperature below 10° C. To this mixture, 2.1 L of 25 w/w % sodium hydroxide solution was added while maintaining the temperature at 5-20° C. The phases were allowed to settle and the upper layer organic was separated. The lower aqueous layer was extracted with of toluene (2×680 mL). The combined organic layers were washed sequentially with water (2×680 mL) and 3.5 M aqueous sodium chloride solution (2×680 mL). The toluene solution was then dried using anhydrous magnesium sulfate (30 g), filtered and concentrated under vacuum to afford 298.1 g of crude (1R,2S)-Ethyl 2-((S)-1-phenylethylamino)cyclohexanecarboxylate (9) free base, as an oil. The crude product was dissolved in 1.1 L of ethyl acetate in a 2 L reactor flask and cooled to −0.5° C. temperature. To this mixture, 247 mL of 30 wt. % hydrogen bromide in propionic acid was added with agitation over 1 h and 20 min, while maintaining the temperature at 0±2° C. The contents were stirred for an additional 1 h at 0° C. and the crystalline product was filtered and washed twice with 300 mL of cold (0° C.) ethyl acetate. The wet cake was dried at 45° C. temperature under vacuum for 5 h to afford 302.3 g of the desired (1R,2S)-Ethyl 2-((S)-1-phenylethylamino)cyclohexanecarboxylate hydrobromide salt (9). The dried hydrobromide salt (9,) and 2.47 L of acetonitrile was added to a 3 L reactor flask under nitrogen then heated to reflux at approximately 81-82° C. temperature. After the solids were dissolved, the clear solution was gradually cooled to 0° C. over 3 h period and held for 30 min at 0±2° C. temperature. The solids were filtered and washed with 200 mL of cold (0° C.) acetonitrile. The wet cake was dried at 40-45° C. temperature under vacuum for 18 h to afford 246.2 g of the purified (1R,2S)-Ethyl 2-((S)-1-phenylethylamino)cyclohexanecarboxylate hydrobromide salt in 69.1% yield, as a white powder. Analytical HPLC (Daicel Chiralpack AD-RH column, Size: 150×4.6 mm); 0.02 M Ammonium acetate buffer (pH: 7.7-7.8): Acetonitrile/50:50, 0.3 mL/min, Wave length: 220 nm, Column oven temperature: 55° C., Rt: 16.14 min, 99.75% (PA); 1H NMR (D2O, 400 MHz): δ 7.56-7.50 (m, 5H), 4.62 (q, 1H, J=10.4, 6.8 Hz), 4.39-4.31 (m, 1H), 4.30-4.22 (m, 1H), 3.27-3.15 (m, 2H), 2.26-2.19 (m, 1H), 1.81-1.64 (m, 3H), 1.70 (d, 3H, J=6.8 Hz), 1.57-1.39 (m, 2H), 1.33 (t, 3 H, J=7.2 Hz), 1.30-1.18 (2H); LC-MS (m/z): 276.2 (M+H)+.