C([Li])CCC.Br[C:7]1[CH:12]=[CH:11][C:10]([S:13]([N:16]2[CH2:20][CH2:19][CH2:18][CH2:17]2)(=[O:15])=[O:14])=[CH:9][CH:8]=1.[B:21](OC(C)C)([O:26]C(C)C)[O:22]C(C)C>O1CCCC1>[N:16]1([S:13]([C:10]2[CH:11]=[CH:12][C:7]([B:21]([OH:26])[OH:22])=[CH:8][CH:9]=2)(=[O:15])=[O:14])[CH2:20][CH2:19][CH2:18][CH2:17]1n-Butyllithium (20 mL, 31 mmol) was added dropwise over 30 min to a cooled (−78° C.) solution of 1-[(4-bromobenzenesulfonyl)pyrrolidine (3.0 g, 10.3 mmol) and triisopropyl borate (7.2 mL, 30.9 mol) in anhydrous tetrahydrofuran (10 mL) under a nitrogen atmosphere. The reaction mixture was stirred for 1 h at −78° C. whereafter the temperature was allowed to reach room temperature over 3 h. Silica gel was added and the solvent was evaporated. Chromatography on a silica gel column using a gradient methylene chloride (100%) to methylene chloride/ethanol, (1:1), gave 1.85 g (70% yield) of the title compound as a white solid: 1H NMR (CD3OD, 400 MHz) δ 7.90 (d, J=7 Hz, 2H), 7.75 (d, J=8 Hz, 2H), 3.21 (m, 4H), 1.72 (m, 4H); 13C NMR (CDCl3/CD3OD (1:1), 100 MHz) δ 136.79, 133.50, 125.48, 47.19, 24.30; MS (ES) m/z 256 (M++1).
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