N-Alkylhydrazones of aliphatic ketones in the synthesis of 1,3,4-trisubstituted non-symmetric pyrazoles

Reactions of N-alkylhydrazones of aliphatic ketones with the Vilsmeier–Haack reagent (DMF–POCl3) were evaluated as a promising approach toward the synthesis of trisubstituted non-symmetric pyrazoles. It was found that either 1,3,4-trialkylpyrazoles or 1,3-dialkylpyrazole-4-carbaldehydes could be obtained in these transformations in high yields (72–83%), in a regioselective manner.