[Cl:1][C:2]1[CH:3]=[C:4]([C:8]2[NH:9][C:10](=[O:13])[O:11][CH:12]=2)[CH:5]=[CH:6][CH:7]=1.C(#N)C.S(=O)(=O)(O)O.[C:22]([O:26][CH3:27])(=[O:25])[CH:23]=[CH2:24]>O>[Cl:1][C:2]1[CH:3]=[C:4]([C:8]2[NH:9][C:10](=[O:13])[O:11][C:12]=2[CH2:24][CH2:23][C:22]([O:26][CH3:27])=[O:25])[CH:5]=[CH:6][CH:7]=1To a solution of 4-(3-chlorophenyl)oxazol-2(3H)-one (3.31 g) and acetonitrile (15 mL) was gradually added conc. sulfuric acid (5.01 g) at 0° C. To the reaction mixture was added methyl acrylate (3.05 mL) at 0° C. and the mixture was stirred at room temperature for 5 hrs. Water was added to the reaction mixture and the mixture was extracted with ethyl acetate-tetrahydrofuran (1:1). The organic layer was washed successively with water and saturated brine, dried over anhydrous magnesium sulfate and concentrated. The residue was subjected to silica gel column chromatography, and methyl 3-[4-(3-chlorophenyl)-2-oxo-2,3-dihydro-5-oxazolyl]propionate (3.0 g, 63%) was obtained as an oil from a fraction eluted with ethyl acetate-hexane (1:1, volume ratio).
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