A method was suggested for preparing previously unknown 3-aryl-substituted pyrazole-4-carboxylic acids, involving Vilsmeier formylation of semicarbazones of 26 available mono-and disubstituted acetophenones and 2-acetylthiophene followed by oxidation of the resulting 3-aryl-substituted pyrazole-4-carboxaldehydes under the action of potassium permanganate. The mechanism of the formylation reaction is discussed. The method successfully works even with acetophenones containing alkyl substituents. In the latter case, an additional stage that involves isolation of pyrazole-4-carboxylic acids as their silyl esters is used.It is known [1] that semicarbazones of certain methyl aryl ketones react with phosphoryl chloride in DMF to form 3-arylpyrazole-4-carboxaldehydes. Taking into account that the pyrazole ring is a constituent of natural amino acids [234], as well as that pyrazolecarboxylic acids are attractive as intermediates in the synthesis of new medicinals and their precursors, we have studied the conversion of a wide range of available methyl aryl ketones I into pre-ÄÄÄÄÄÄÄÄÄÄÄÄ viously unknown 3-arylpyrazole-4-carboxylic acids VI via the intermediate Vismeier formylation of semicarbazones II to pyrazolecarboxaldehydes III, and oxidation of the latter with potassium permanganate.It was found that available semicarbazones II, as would be expected, are formylated under the action of 2 mol of POCl 3 3DMF complex IV to form the corresponding 3-arylpyrazole-4-carboxaldehydes III.

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Formylation of ten accessible phenylhydrazones and semicarbazones derived from alkyl, benzyl, and cycloalkyl methyl ketones with the complex of POCl 3 with dimethylformamide was studied. Depending on the electronic and steric structure of the substrates, the reaction yields 1-phenyl-or 1-unsubstituted 3,4-dialkyl-, 3-alkyl-4-aryl-, or 3-alkyl-4-formylpyrazoles. These compounds can be readily oxidized into the corresponding carboxylic acids.It is known [13 4] that phenylhydrazones and semicarbazones derived from aryl methyl ketones enter into the Vilsmeier reaction with the complex POCl 3 3 HC(O)N(CH 3 ) 2 (I) to give 3-arylpyrazol-4-carboxal-ÄÄÄÄÄÄÄÄÄÄÄÄ dehydes via the sequence of two attacks by complex I: first at the CH 3 group of the substrate with the subsequent cyclization into 3-arylpyrazoles and then at the C 4 atom of the resulting heterocycles: ArC(CH 3 )=NNHC(O)NH 2 776 I

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