Br[C:2]1[CH:7]=[CH:6][CH:5]=[C:4]([F:8])[CH:3]=1.[Mg].II.[CH3:12][O:13][C:14](=[O:28])[C@H:15]1[CH2:19][CH2:18][C:17](=[O:20])[N:16]1[C:21]([O:23][C:24]([CH3:27])([CH3:26])[CH3:25])=[O:22]>C1COCC1>[CH3:12][O:13][C:14](=[O:28])[C@H:15]([NH:16][C:21]([O:23][C:24]([CH3:26])([CH3:25])[CH3:27])=[O:22])[CH2:19][CH2:18][C:17]([C:2]1[CH:7]=[CH:6][CH:5]=[C:4]([F:8])[CH:3]=1)=[O:20]
To a mixture of 1-bromo-3-fluorobenzene (0.79 g, 4.5 mmol) and magnesium turnings (0.12 g, 5.0 mmol) in anhydrous THF (8 mL) was added a small piece of iodine. The mixture was heated at reflux for 2 hr and no magnesium turnings left. The solution was cooled to 0° C. and transferred into a stirred solution of N-Boc-D-pyroglutamic acid methyl ester (0.80 g, 3.3 mmol) in anhydrous THF (4 mL) at −40° C. under argon atmosphere. After stirring at −40° C. for 1 hr and then at 0° C. for 1 hr, the reaction was quenched with 8 mL of 1:1 HOAc/MeOH and the mixture diluted with Et2O (40 mL). The organic layers were washed with water and brine, dried (Na2SO4) and concentrated under vacuum. Purification by silica gel chromatography (10–20% EtOAc/hexanes) gave 0.57 g (51%) of (2R)-2-tert-butoxycarbonylamino-5-(3-fluoro-phenyl)-5-oxo-pentanoic acid methyl ester as a white solid. 1H NMR (CDCl3, 300 MHz) δ 7.82 (1H, d), 7.75 (1H, d), 7.56 (1H, q), 7.38 (1H, t), 5.30 (1H, br.d), 4.50 (1H, br.s), 3.87 (3H, s), 3.20 (2H, m), 2.45 (1H, m), 2.20 (1H, m), 1.54 (9H, s).
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