[Br:1][C:2]1[CH:15]=[CH:14][C:5](/[CH:6]=[N:7]/[S@@:8]([C:10]([CH3:13])([CH3:12])[CH3:11])=[O:9])=[CH:4][CH:3]=1.[Li][C:17]1[CH:18]=[CH:19][CH:20]=[CH:21][CH:22]=1>C1COCC1>[Br:1][C:2]1[CH:15]=[CH:14][C:5]([C@@H:6]([C:17]2[CH:18]=[CH:19][CH:20]=[CH:21][CH:22]=2)[NH:7][S@@:8]([C:10]([CH3:11])([CH3:12])[CH3:13])=[O:9])=[CH:4][CH:3]=1(R,E)-N-(4-bromobenzylidene)-2-methylpropane-2-sulfinamide, 18-b, (10 g, 34.84 mmol) was dissolved in anhydrous THF (100 ml). The mixture was then cooled to −78° C. and PhLi (34.84 ml, 69.68 mmol) was added dropwise. After addition the mixture was allowed to stir at −78° C. for additional 4 h and warmed to room temperature for another 2 h. The reaction was TLC monitored and prolonged the time if necessary. 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=2/1) to provide the product, 23-a, (8 g, 63%). HPLC indicated that the diastereomer ratio is 80:20 and recrystallization once in hexane/ethyl acetate can increase it to above 95:5 with around 40% material lost in the mother liquid.
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