CS(Cl)(=O)=O.O[C:7]1([C:18]([O:20][CH2:21][CH3:22])=[O:19])[CH2:11][O:10][C:9]2[CH2:12][CH2:13][CH2:14][CH2:15][C:16](=[O:17])[C:8]1=2.C(N(CC)CC)C.O>ClCCl>[O:17]=[C:16]1[C:8]2[C:7]([C:18]([O:20][CH2:21][CH3:22])=[O:19])=[CH:11][O:10][C:9]=2[CH2:12][CH2:13][CH2:14][CH2:15]1Methanesulfonyl chloride (9.7 g, 0.08 mol) was added dropwise to a stirring solution of ethyl 3-hydroxy-4-oxo-2,3,5,6,7,8-hexahydro-4H-cyclohepta[b]furan-3-carboxylate (17 g, 0.07 mol) and triethylamine (30 mL, 0.21 mol) in dichloromethane (100 mL) at 0° C. The mixture was allowed to reach ambient temperature, stirred for 2 hours, then poured into water and extracted with dichloromethane. The organic layer was washed sequentially with aqueous 2N sodium hydroxide, saturated aqueous sodium bicarbonate, and brine, then dried over magnesium sulfate, filtered, concentrated in vacuo, and purified on Silica gel (1:1 ethyl acetate/hexanes) to give the title compound.
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