[C:1]([CH2:3][C:4]([O:6][CH3:7])=[O:5])#[N:2].[Cl:8][C:9]1[C:13]([Cl:14])=[C:12]([C:15](Cl)=[O:16])[S:11][N:10]=1.Cl>O1CCCC1>[C:1]([CH:3]([C:15]([C:12]1[S:11][N:10]=[C:9]([Cl:8])[C:13]=1[Cl:14])=[O:16])[C:4]([O:6][CH3:7])=[O:5])#[N:2]To a solution of methyl cyanoacetate (1.98 g) in unhydrous tetrahydrofuran (20 ml) 60% sodium hydride (1.6 g) was added at a temperature below 10° C. To the reaction mixture a solution of 3,4-dichloro-5-isothiazolecarbonyl chloride (4.30 g) in unhydrous tetrahydrofuran (15 ml) was added dropwise at the same temperature. After finishing the addition, the reaction mixture was stirred at room temperature for 2 hours and 1N-aqueous hydrochloric acid (10 ml) was added. After extraction with ethyl acetate and drying the organic phase with unhydrous sodium sulfate, the solvent was distilled off under reduced pressure to obtain methyl 2-cyano-3-(3,4-dichloro-5-isothiazolyl)-3-oxopropanoate (4.7 g) as pale yellow crystals. mp 119-122° C.
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