Abstract The major products from the reaction of β-alkoxyvinyl trifluoromethyl ketones 1a-c with methylhydrazine (2) in absolute ethanol are the 3-(trifluoromethyl)-substituted-1- methylpyrazoles 3a-3c with lesser amounts of the 5-(trifluoromethyl)-substituted products 4a- 4c and 5a-5c. Carrying out the reaction in non-polar, aprotic solvents can further enhance the regioselectivity favoring the 3-(trifluoromethyl)-substituted isomers.
