Abstract It was established that the reaction of 3-aryl-1-(2-methyloxiran-2-yl) prop-2-en-1- ones with tosylhydrazine leads to 3-[(E)-2-arylvinyl]-4-methyl-1-tosyl-1H-pyrazoles and 3- aryl-1-(2-methyloxiran-2-yl)-3-tosylpropan-1-ones. The latter are formed as a result of