[N:1]([CH2:4][CH2:5][O:6][CH2:7][CH2:8]OS(C1C=CC(C)=CC=1)(=O)=O)=[N+:2]=[N-:3].C1C=C(Cl)C=[C:22]([C:27]([O:29]O)=O)C=1.[OH:31][S:32]([O-])=[O:33].[Na+]>C(Cl)Cl>[N:1]([CH2:4][CH2:5][O:6][CH2:7][CH2:8][S:32]([CH2:22][CH2:27][OH:29])(=[O:33])=[O:31])=[N+:2]=[N-:3]A solution of sulfide 3 (8.41 g, 44 mmol) in CH2Cl2 (100 ml) was cooled in an ice bath. mCPBA (84% purity, 27.1 g, 3 equiv.) was added portion wise and the resulting solution was stirred at RT for 16 h. An aqueous 1 M NaHSO3 solution (20 ml) was added, and the resulting suspension was vigorously stirred at RT for 30 min. The white m-chlorobenzoic acid precipitate was filtrated over a celite pad. The organic layer was washed with a saturated aqueous NaHCO3 solution (3×20 ml), dried over MgSO4, filtrated then concentrated under reduced pressure. Purification by flash column chromatography (eluent: pet. ether/AcOEt 1:1 then 3:7 then pure AcOEt) afforded sulfone 5 as a colorless liquid (8.41 g, 86%).
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