First synthesis of 3-aryl-5-dichloromethyl-2-pyrazolines. The electrochemical generation of 2,2-dichlorovinylacetophenones as a key step

An efficient synthetic route to the title compounds has been established. Chloralacetophenones 2 were prepared by treatment of acetophenones 1 with anhydrous chloral. Dehydration of intermediates 2 under acidic conditions yielded 2,2,2-trichloroethylideneacetophenones 3, which were transformed to 2,2-dichlorovinylacetophenones 5 in nearly quantitative yields by selective electrochemical monodechlorination at either mercury or graphite electrodes. Finally, 3-aryl-5-dichloromethyl-2-pyrazolines 7 were efficiently obtained on treatment of compounds 5 with either hydrazine or methylhydrazine.