Regioselective synthesis of unsymmetrical 3, 5-dialkyl-1-arylpyrazoles

3-Alkoxylmethyl-5-alkylpyrazoles undergo regioselective N-arylation with 4-fluoronitrobenzene in the presence of base to yield the corresponding 1-(4-nitro-phenyl)pyrazoles. Further elaboration of these intermediates furnishes a practical synthesis of unsymmetrical 3,5-dialkyl-1-arypyrazoles. A tentative explanation of the observed regioselectivities is provided.