Synthesis method of 3-(difluoromethyl)-1-methyl-1H-pyrazole-4-carboxylic acid

The invention discloses a synthesis method of 3-(difluoromethyl)-1-methyl-1H-pyrazole-4-carboxylic acid, which comprises the following specific steps: in an organic solvent, carrying out cyclization on diformyl ethyl acetate and methylhydrazine sulfate, and reacting at low temperature for 6-12 hours to obtain a cyclization product compound I; then adding the compound I and a difluoromethylation reagent [bis (difluoroacetoxy) iodine] benzene in an inert gas atmosphere, and reacting for 12-24 hours at room temperature under the illumination of a blue 18W LED lamp to generate 3-(difluoromethyl)-1-methyl-1H-pyrazole-4-carboxylic acid ethyl ester (compound II); and finally, hydrolyzing under an alkaline condition to obtain the 3-(difluoromethyl)-1-methyl-1H-pyrazole-4-carboxylic acid (compound III). The method does not need a catalyst, is safe and easy to control in process, mild in synthesis condition, simple and rapid in reaction step, good in reaction selectivity and high in target product yield, and has relati