[C:1]([O:5][C:6]([N:8]1[CH2:13][CH2:12][C:11]([C:17]2[CH:22]=[CH:21][C:20]([F:23])=[CH:19][CH:18]=2)([C:14](O)=[O:15])[CH2:10][CH2:9]1)=[O:7])([CH3:4])([CH3:3])[CH3:2].O1CCCC1.B.CO>O1CCCC1.C(OCC)(=O)C>[F:23][C:20]1[CH:19]=[CH:18][C:17]([C:11]2([CH2:14][OH:15])[CH2:10][CH2:9][N:8]([C:6]([O:5][C:1]([CH3:2])([CH3:3])[CH3:4])=[O:7])[CH2:13][CH2:12]2)=[CH:22][CH:21]=1
1-(tert-Butoxycarbonyl)-4-(4-fluorophenyl)piperidine-4-carboxylic acid (9.5 g, 29.3 mmol) was suspended in tetrahydrofuran (60 mL) and cooled to 0° C. To this solution was added borane tetrahydrofuran complex (1 M in tetrahydrofuran, 59 mL, 59 mmol) cautiously over 15 min. The reaction mixture was allowed to warm to room temperature overnight and then heated at reflux for 24 h. The mixture was cooled to 0° C., treated with excess methanol, diluted with ethyl acetate, washed with 1 N sodium hydroxide (2×), then brine (2×), dried over sodium sulfate, and concentrated. Column chromatography on silica gel (40% ethyl acetate/hexanes) gave 6.6 g (72%) as a white powder. 1H-NMR (CDCl3, 300 MHz) 7.24-7.29 (m, 2H), 7.00-7.05 (m, 2H), 3.66-3.71 (m, 2H), 3.49 (s, 2H), 2.96-3.05 (m, 2H), 2.06-2.10 (m, 2H), 1.69-1.77 (m, 2H), 1.40 (s, 9H). Mass spec.: 310.21 (MH)+.
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