N,N-dimethylformamide catalyzed electrophilic/nucleophilic chlorination of pyrazoles was written by Liu, Yuanyuan;Li, Yi;Zhang, Zhenglin;Xu, Guanghui;Li, Jie;Gao, Shang. And the article was included in Nanjing Gongye Daxue Xuebao, Ziran Kexueban in 2014.Category: pyrazoles-derivatives This article mentions the following:
With N,N-Dimethylformamide (DMF) as a catalyst, 1-phenyl-5-(p-tolyl)-1H-pyrazol-3-ol (1a) was heated to reflux in thionyl chloride (SOCl2) and 4-chloro-1-phenyl-5-(p-tolyl)-1H-pyrazol-3-ol (2a) was obtained in the yield of 83%. High performance liquid chromatog. (HPLC) anal. of the reaction mixture revealed that the optimized conditions were n(1a) : n(DMF) of 10:1, and refluxing in SOCl2 for 4 h. During the column chromatog. purification, elemental sulfur was isolated. The DMF-catalyzed electrophilic/nucleophilic chlorination mechanism was proposed, and pyrazole substrates 1b-1h were prepared to explore the scope of the mechanism. The structures of chlorinated products 2b-2h were characterized by NMR hydrogen spectrum (1H NMR), NMR carbon spectrum (13C NMR), and elemental anal. The structure of 2d was also determined by single-crystal X-ray diffraction anal. This chlorination reaction was simple to be operated and had good functionality tolerance. In the experiment, the researchers used many compounds, for example, 4-Chloro-3,5-dimethyl-1H-pyrazole (cas: 15953-73-8Category: pyrazoles-derivatives).
4-Chloro-3,5-dimethyl-1H-pyrazole (cas: 15953-73-8) belongs to pyrazole derivatives. The strategies for the synthesis of pyrazoles generally can be applied for the construction of indazoles. Protonation of pyrazole in strong acid leads to pyrazolium cations, which undergo electrophilic substitution preferentially at C3 rather than C4. The pyrazole anion is not reactive toward nucleophiles but is mostly reactive to electrophiles.Category: pyrazoles-derivatives
Referemce:
Pyrazole – Wikipedia,
Pyrazoles – an overview | ScienceDirect Topics