A REGIOSELECTIVE SYNTHESIS OF 5-CHLORO-1-VINYLAND 3-ALKENYL-5-CHLORO-1H-PYRAZOLES

Abstract

The reaction of 2,2-dichlorovinyl ketones with 2-(hydroxyethyl)hydrazine led to the formation of 3-substituted 5-chloro-1-(2-hydroxyethyl)-1Н-pyrazoles. Heating 1-(2-hydroxyethyl)-1H-pyrazoles in CHCl₃ under reflux in the presence of thionyl chloride gave rise to 5-chloro-1-(2-chloroethyl)-1H-pyrazoles. 5-Chloro-1-vinyl-1Н-pyrazoles were obtained by elimination of hydrogen chloride from the corresponding 5-chloro-1-(2-chloroethyl)-1Н-pyrazoles by the action of NaOH in EtOH or t-BuOK in pyridine. The synthesis of 5-chloro-3-propyl-1-vinyl-1H-pyrazole-4-carbaldehyde was carried out by the treatment of 5-chloro-1-(2-chloroethyl)-3-propyl-1H-pyrazole-4-carbaldehyde with t-BuOK in pyridine. 3-Alkenyl-5-chloro-1-(2-chloroethyl)-1H-pyrazoles were formed as a result of the elimination of HCl from the corresponding 3-(α-chloroalkyl)-1H-pyrazoles in DMF at 150°C.

Authors: Valentina А. Kobelevskaya*, Ludmila I. Larina, Alexandr V. Popov