[CH2:1]([O:3][C:4]([C:6]1[CH2:10][CH2:9][CH2:8][C:7]=1[NH:11][CH2:12][CH2:13][C:14]([CH3:17])([CH3:16])[CH3:15])=[O:5])[CH3:2].B.N1C=CC=CC=1.C(OC([C@@H]1CCC[C@H]1NCCC(C)(C)C)=O)C>C(O)(=O)C>[CH2:1]([O:3][C:4]([C@@H:6]1[CH2:10][CH2:9][CH2:8][C@@H:7]1[NH:11][CH2:12][CH2:13][C:14]([CH3:15])([CH3:17])[CH3:16])=[O:5])[CH3:2]To a solution of 2-(3,3-dimethylbutylamino)-cyclopent-1-enecarboxylic acid ethyl ester (5.59 g, 23.4 mmol) in acetic acid (70 mL) was added a 8.0 M solution of borane in pyridine (3.2 mL, 25.6 mmol) at 25° C. After stirring for 15 min, the reaction mixture was concentrated in vacuo. The crude material was triturated with 1.0 M aqueous hydrochloric acid solution (25 mL) and stirred for 0.5 h (until the gas evolution ceased). The mixture was extracted with ethyl acetate (3×50 mL) and the combined organic layers were dried over anhydrous magnesium sulfate and concentrated in vacuo. The crude material was purified by flash column chromatography (Teledyne Isco RediSep Flash Column; 0-10% methanol in dichloromethane) to afford cis-2-(3,3-dimethylbutylamino)-cyclopentanecarboxylic acid ethyl ester as a yellowish oil (0.40 g, 1.7 mmol, 7%) and trans-2-(3,3-dimethylbutylamino)-cyclopentanecarboxylic acid ethyl ester and an off-white solid (2.37 g, 9.8 mmol, 42%). cis-2-(3,3-Dimethylbutylamino)-cyclopentanecarboxylic acid ethyl ester: 1H NMR (400 MHz, CDCl3) δ 0.91 (9H, s), 1.28 (3H, t, J=7.0 Hz), 1.35-1.50 (2H, m), 1.56-1.73 (2H, m), 1.80-2.03 (4H, m), 2.60-2.75 (2H, m), 2.98-3.02 (1H, m), 3.35 (1H, q, J=7.4 Hz), 4.15 (2H, q, J=6.9 Hz), 6.38 (1H, s). trans-2-(3,3-Dimethylbutylamino)-cyclopentanecarboxylic acid ethyl ester: 1H NMR (400 MHz, CDCl3) δ 0.94 (9H, s), 1.29 (3H, t, J=7.0 Hz), 1.66-2.01 (6H, m), 2.11-2.27 (2H, m), 2.86 (2H, t, J=8.6 Hz), 3.10 (1H, q, J=7.8 Hz), 3.68 (1H, q, J=7.0 Hz), 4.18 (2H, q, J=7.0 Hz). LC-MS (ESI) calcd for C14H27NO2 241.20, found 242.4 [M+H+].
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