[O:1]1[CH2:5][CH2:4]NC1=O.Br[CH:8]([C:14]([O:16][CH2:17][CH3:18])=[O:15])[C:9]([O:11][CH2:12][CH3:13])=[O:10].[C:19](=[O:22])([O-])[O-].[K+].[K+].[CH3:25][C:26]([CH3:28])=O>>[O:22]1[C:19]2[CH:25]=[CH:26][CH:28]=[CH:4][C:5]=2[O:1][C:8]1([C:14]([O:16][CH2:17][CH3:18])=[O:15])[C:9]([O:11][CH2:12][CH3:13])=[O:10]A mixture of 240 mg of the above oxazolidinone, 234 mg of diethyl bromomalonate, 450 mg of anhydrous potassium carbonate and 10 ml of acetone is stirred overnight, filtered, washed with acetone and evaporated to a brown oil. The oil is purified by flash chromatography, eluting with 5 percent acetone in toluene. The pure fractions are combined and evaporated giving 237 mg of (R,R)-5-(3-chlorophenyl)-2-oxo-3-oxazolidinyl)propyl)-1,3-benzodioxole-2,2-dicarboxylic acid, diethyl ester as a colorless oil.
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