C[Si]([N-][Si](C)(C)C)(C)C.[Li+].[CH3:11][O:12][C:13](=[O:25])[CH:14]([S:16]([C:19]1[CH:24]=[CH:23][CH:22]=[CH:21][CH:20]=1)(=[O:18])=[O:17])[CH3:15].[Br:26][CH2:27][CH2:28][CH2:29]Br>O1CCCC1>[CH3:11][O:12][C:13](=[O:25])[C:14]([S:16]([C:19]1[CH:24]=[CH:23][CH:22]=[CH:21][CH:20]=1)(=[O:17])=[O:18])([CH3:15])[CH2:29][CH2:28][CH2:27][Br:26]A solution of lithium bis(trimethylsilyl)amide in tetrahydrofuran (1M, 6.6 ml, 6.6 mmol) was added dropwise to a stirred solution of 2-benzenesulfonylpropionic acid methyl ester (1.38 g, 5.7 mmol) in tetrahydrofuran at −78° C. The mixture was stirred for 30 min. and 1,3-dibromopropane (3.17 ml, 31.2 mmol) was added. The mixture was slowly warmed to room temperature and stirred for 4 days. After quenching with satd. aqueous NH4Cl, the mixture was extracted into dichloromethane. The combined organic extracts were dried (Na2SO4) and concentrated. The residue was purified on silica gel (i-hexane-ethyl acetate 5–20%) to give the title product (330 mg, 15%).
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