[Cl:1][C:2]1[CH:3]=[C:4]([C:7](=[O:9])[CH3:8])[S:5][CH:6]=1.CO[CH:12](OC)[N:13]([CH3:15])[CH3:14]>>[Cl:1][C:2]1[CH:3]=[C:4]([C:7](=[O:9])[CH:8]=[CH:12][N:13]([CH3:15])[CH3:14])[S:5][CH:6]=1A mixture of 1-(4-chloro-2-thienyl)ethanone (32.1 mmol) and N,N-dimethylformamide dimethyl acetal (112.2 mmol) was refluxed for 3 h and then allowed to cool to room temperature whereupon crystallization occurred. The reaction mixture was stored in a freezer at −18° C. for 2 h. The supernatant liquid was decanted, the crystals were dried in vacuum to afford 5.3 g (77% yield) of 1-(4-chloro-2-thienyl)-3-(dimethylamino)prop-2-en-1-one which was used in the next step without further purification.
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