[CH3:1][S:2][CH2:3][S:4](=[O:6])[CH3:5].O1[CH2:11][CH2:10][CH2:9][CH2:8]1.[H-].[Na+].BrCCCCBr>C(Cl)Cl>[CH3:1][S:2][C:3]1([S:4](=[O:6])[CH3:5])[CH2:11][CH2:10][CH2:9][CH2:8]1
Formaldehyde dimethyl mercaptal S-oxide (1.49g) was dissolved in 15 ml. of tetrahydrofuran, and with ice cooling, 665 mg of sodium hydride was added. The mixture was stirred for 30 minutes with ice cooling, and then 2.936g of 1,4-dibromobutane was added. The mixture was stirred for 1 hour with ice cooling, for 24 hours at room temperature, and then for 44.5 hours at 50° C. Then, 100 ml. of methylene chloride was added, and the insoluble matter was separated. The filtrate was concentrated at reduced pressure, and the residue was separated by column chromatography (silica gel, eluted with 20% AcOEt-CH2Cl2, AcOEt, and MeOH) to afford 985 mg of cyclopentanone dimethyl mercaptal S-oxide. Also, 463 mg of formaldehyde dimethyl mercaptal S-oxide was recovered. The yield was 46%, and the conversion was 67%.
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