C[O-].[Na+].C[O:5][C:6](=O)[CH2:7][S:8][CH:9]([CH3:15])[CH2:10][C:11]([O:13][CH3:14])=[O:12].C(O)(=O)C.C([O-])([O-])=O.[Na+].[Na+]>C1(C)C=CC=CC=1>[CH3:15][CH:9]1[CH:10]([C:11]([O:13][CH3:14])=[O:12])[C:6](=[O:5])[CH2:7][S:8]1
To a suspension of sodium methoxide (5.89 g, 109.2 mmol) in toluene (150 mL) was added methyl 3-(2-methoxy-2-oxoethylthio)butanoate (150 g, 72.8 mmol) dropwise. The resultant mixture was heated to reflux and stirred overnight. The resulting reaction mixture was cooled then poured into a mixture of 10.0 mL of acetic acid in 150.0 g of crushed ice. The solution was made basic (pH=8-9) by addition of saturated Na2CO3 and the resulting mixture extracted with ethyl acetate. The combined organic layers were then combined and washed with brine, dried over anhydrous Na2SO4, filtered, evaporated, and the residue purified by column chromatography (eluent: petroleum ether/ethyl acetate=20/1-5/1) to provide methyl 2-methyl-4-oxo-tetrahydrothiophene-3-carboxylate as a colorless oil (4.0 g, 32%).
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