[Cl:1][C:2]1[CH:7]=[CH:6][C:5]([C:8]2[NH:9][C:10](=[O:13])[O:11][CH:12]=2)=[CH:4][CH:3]=1.S(=O)(=O)(O)O.[C:19]([O:23][CH3:24])(=[O:22])[CH:20]=[CH2:21].O>C(#N)C>[Cl:1][C:2]1[CH:3]=[CH:4][C:5]([C:8]2[NH:9][C:10](=[O:13])[O:11][C:12]=2[CH:20]([CH3:21])[C:19]([O:23][CH3:24])=[O:22])=[CH:6][CH:7]=1To a solution of 4-(4-chlorophenyl)-2-oxo-4-oxazoline (794.3 g) in acetonitrile (2383 mL) was added dropwise conc. sulfuric acid (1195 g) under ice-cooling at not higher than 10° C. Then methyl acrylate (731 mL) was added at not higher than 10° C., and the mixture was taken out from an ice-bath and stirred at room temperature for 3 h. Water (7.94 L) was added under ice-cooling at not higher than 20° C. The precipitated crystals were collected by filtration and washed successively with 1% aqueous sodium hydrogencarbonate, water, isopropyl ether to give methyl 2-(4-(4-chlorophenyl)-2-oxo-4-oxazolin-5-yl)propionate (1017.8 g; yield 89%). Recrystallization from methanol gave colorless crystals.
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