[C:1]1([S:7][CH:8]2[CH2:11][CH:10]([C:12]([O:14][CH3:15])=[O:13])[CH:9]2[C:16]([O:18][CH3:19])=[O:17])[CH:6]=[CH:5][CH:4]=[CH:3][CH:2]=1.[OH:20]OS([O-])=O.[K+].[K+].S(=O)(=O)([O-])[O-].[K+].S([O-])(OO)(=O)=O.[K+].[OH2:40]>CO.ClCCCl>[C:1]1([S:7]([CH:8]2[CH2:11][CH:10]([C:12]([O:14][CH3:15])=[O:13])[CH:9]2[C:16]([O:18][CH3:19])=[O:17])(=[O:20])=[O:40])[CH:2]=[CH:3][CH:4]=[CH:5][CH:6]=1To a vigorously stirred solution of 1.05 g (3.75 mmol) of dimethyl 3-(phenylthio)cyclobutane-1,2-dicarboxylate from Step A in 20 mL of methanol, was added slowly a suspension of 3.46 g (11.25 mmol) of OXONE (a commercially available mixture of sulfuric acid potassium salt and potassium hydrogen peroxymonosulfate) in 20 mL of water. The resultant cloudy suspension was stirred for 0.5 h then diluted with 50 mL of water and 100 mL of 1,2-dichloroethane. The phases were allowed to separate and the aqueous phase was extracted with 20 mL of 1,2-dichloroethane. The combined organic layers were washed with 2×50 mL of dilute aqueous sodium bicarbonate solution, 2×50 mL of water and 50 mL of brine, dried over anhydrous magnesium sulfate and concentrated to give 1.10 g (94% yield) of the title compound as a viscous oil; EI-MS, m/e (relative intensity): 281 (M+ -OCH3, 9), 171 (100), 139 (24), 111 (47); 1H NMR (CDCl3) δ 2.48 (m, 1H), 2.76 (m, 1H), 3.23 (q, 1H), 3.52 (s, 3H), 3.74 (s, 3H), 3.80 (m, 1H), 3.92 (q, 1H), 7.58 (m, 2H), 7.68 (m, 1H), 7.89 (m, 2H).
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