Br[C:2]1[CH:7]=[CH:6][C:5]([Br:8])=[CH:4][CH:3]=1.[Li]CCCC.[F:14][C:15]1[CH:28]=[C:27]([F:29])[CH:26]=[CH:25][C:16]=1/[CH:17]=[N:18]/[S@:19]([C:21]([CH3:24])([CH3:23])[CH3:22])=[O:20]>C1COCC1>[Br:8][C:5]1[CH:6]=[CH:7][C:2]([C@@H:17]([C:16]2[CH:25]=[CH:26][C:27]([F:29])=[CH:28][C:15]=2[F:14])[NH:18][S@:19]([C:21]([CH3:24])([CH3:23])[CH3:22])=[O:20])=[CH:3][CH:4]=11,4-dibromobenzene (10.58 g, 44.8 mmol) was dissolved in THF (150 ml) and cooled to −78° C. under nitrogen. Then n-BuLi (18 ml, 44.8 mmol) was added dropwise below −60° C. After addition, the mixture was stirred at −78° C. for additional 1 h and then (S,E)-N-(2,4-difluorobenzylidene)-2-methylpropane-2-sulfinamide, 21-a, (10 g, 40.77 mmol) in anhydrous THF was added dropwise below −60° C. Then the mixture was allowed to stir at room temperature for 6 h. The mixture was quenched with saturated NH4Cl followed by extraction with ethyl acetate. The organic layer was dried over sodium sulfate and concentrated under vacuum. The residue was purified by column chromatography (petroleum ether/ethyl acetate=4/1) to provide the product, 21-b, (7.5 g, 42%). HPLC implicated that only the single isomer was formed.
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