[CH3:1][O:2][N:3]=[C:4]([C:10](=[O:13])[CH2:11][Cl:12])[C:5]([O:7][CH2:8][CH3:9])=[O:6].[CH2:14](O)[CH2:15][OH:16].C1(C)C=CC(S(O)(=O)=O)=CC=1>C1(C)C=CC=CC=1>[CH3:1][O:2][N:3]=[C:4]([C:10]1([O:16][CH2:15][CH2:14][O:13]1)[CH2:11][Cl:12])[C:5]([O:7][CH2:8][CH3:9])=[O:6]A mixture of ethyl 2-methoxyimino-3-oxo-4-chlorobutyrate (syn isomer, 41 g), ethylene glycol (24.6 g), p-toluenesulfonic acid (2.0 g) and toluene (250 ml) was heated for 20 hours under reflux while removing water. The reaction mixture was cooled to ambient temperature, washed with a saturated aqueous solution of sodium bicarbonate, a saturated aqueous solution of sodium chloride in turn, dried over magnesium sulfate and then the solvents were removed. The residue was distilled under reduced pressure to give ethyl 2-methoxyimino-3,3-ethylenedioxy-4-chlorobutyrate (syn isomer, 24.4 g), bp 103°-110° C./2 mmHg.
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