Ambident polyfluoroalkyl-substituted pyrazoles in the methylation reactions

[Display omitted] •The methods for the regioselective methylation of polyfluoroalkylpyrazoles have been developed.•The mechanism of methylation under different conditions was proposed.•The mechanism of methylation was confirmed using the quantum-chemical methods. The reactivity of polyfluoroalkyl-containing pyrazoles has been estimated using the quantum chemical calculations. A good regioselectivity in the methylation of polyfluoroalkylpyrazoles was reached while varying the reaction conditions. Under basic conditions, methylation of such pyrazoles led to the preferred formation of 3-RF-pyrazoles, whereas the use of dimethyl sulfate in the absence of a base resulted in the predominant formation of 5-RF-pyrazoles. A proposed mechanism of methylation was discussed.