[OH:1][CH2:2][C@H:3]([NH:16][C:17](=[O:23])[O:18][C:19]([CH3:22])([CH3:21])[CH3:20])[CH2:4][CH2:5][C:6]1[CH:11]=[CH:10][C:9]([C:12]([F:15])([F:14])[F:13])=[CH:8][CH:7]=1.[O-:24]I(=O)(=O)=O.[Na+].CC(O)C.Cl>CC(C)=O.O.[Ru]=O>[C:19]([O:18][C:17]([NH:16][C@H:3]([CH2:4][CH2:5][C:6]1[CH:7]=[CH:8][C:9]([C:12]([F:15])([F:14])[F:13])=[CH:10][CH:11]=1)[C:2]([OH:24])=[O:1])=[O:23])([CH3:20])([CH3:22])[CH3:21]To a solution of tert-butyl (1R)-1-(hydroxymethyl)-3-[4-(trifluoromethyl)phenyl]propylcarbamate IV (41.3 g; 0.124 mol) in 60% aqueous acetone was added a solid sodium (meta)periodate (266 g; 1.24 mol) followed by ruthenium(II) oxide hydrate (1.65 g; 12.4 mmol). The greenish suspension was stirred for 3 h before adding propan-2-ol (500 mL) and stirring for an additional 30 min to consume excess oxidant. The resulting suspension was filtered through Celite, and the filtrate was concentrated under reduced vacuum to give a brown oil. To the brown foam was added 1 N HCl to pH=1 which was followed by extraction with EtOAc. The organic layer was washed with brine and dried with MgSO4. The crude residue was then purified on a silica gel column (10:1 hexane:EtOAc) to obtain (2R)-2-[(tert-butoxycarbonyl)amino]-4-[4-(trifluoromethyl)phenyl]butanoic acid V (18 g; 51.8 mmol, 42% yield). 1H NMR (CDCl3) 1.46 (brs, 9H), 1.93-2.30 (m, 2H), 2.68-2.87 (m, 2H), 4.12-4.47 (m, 1H), 5.04-5.23 (m, 1H), 7.30 (d, J=8, 2H), 7.55 (d, J=8, 2H); ESIMS found for C16H20F3NO4 m/z 348.3 (M+H).
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