2,2-dichlorovinulketones-based 5-chloro-3-styryl-1<i>H</i>-pyrazoles synthesis

Abstract

Condensation of 4,4-dichlorobut-3-en-2-one with aromatic aldehydes in the presence of catalytic amounts of sulfuric acid leads to the formation of 1,1-dichloro-5-(4-R-phenyl)penta-1,4-diene-3-ones. The reaction of 1,4-dien-3-ones with hydrazines proceeds chemo- and regioselectively under mild conditions with the formation of ( E )-1-methyl-3-styryl-5-chloro-1 H -pyrazoles with a yield reaching 81%. 4-Bromo-1,1-dichloro-5-(4-methoxyphenyl)penta-1,4-dien-3-one reacts with dimethylhydrazine to give 3-[1-bromo-2-(4-methoxyphenyl)vinyl]-5chloro-1-methyl-1 H -pyrazole, which in the presence of KF in DMSO at 120°C forms 1-methyl-3-[(4-methoxyphenyl)ethynyl]-5-chloro-1 H -pyrazole with 69% yield. The structure of the synthesized compounds has been confirmed using IR, NMR spectroscopies, mass spectrometry, and elemental analysis.