[Cl:1][C:2]1[CH:3]=[C:4]([NH:9][NH2:10])[CH:5]=[CH:6][C:7]=1[Cl:8].CO[CH:13](OC)[CH2:14][C:15](=O)[CH3:16]>CCO.O>[Cl:1][C:2]1[CH:3]=[C:4]([N:9]2[CH:13]=[CH:14][C:15]([CH3:16])=[N:10]2)[CH:5]=[CH:6][C:7]=1[Cl:8].[Cl:1][C:2]1[CH:3]=[C:4]([N:9]2[C:15]([CH3:16])=[CH:14][CH:13]=[N:10]2)[CH:5]=[CH:6][C:7]=1[Cl:8]A solution of of 3,4-dichlorophenylhydrazine (4.27 g, 20.0 mmol) in EtOH (50 ml) and H2O (50 ml) was treated with 3-oxobutyraldehyde dimethyl acetal (2.64 g, 20.0 mmol) and refluxed for 1 h. The alcohol was removed in vacuo and the aqueous residue was extracted with AcOEt (2×150 ml). The organic phase was dried (Na2SO4), filtered and evaporated. The remaining oil was chromatographed [silica, elution with gradient hexane to 10% (hexane/AcOEt=1:1)] to obtain 3.01 g (66%) of 1-(3,4-dichloro-phenyl)-3-methyl-1H-pyrazole [Mp. 57-58° C. (AcOEt/hexane), MS: m/e=226 (M+)] as off-white crystals and 1.32 g (29%) of 1-(3,4-dichloro-phenyl)-5-methyl-1H-pyrazole [Mp. 46-47° C. (hexane), MS: m/e=226 (M+)] as white crystals.
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