Straightforward and regiospecific synthesis of pyrazole-5-carboxylates from unsymmetrical enaminodiketones

Article abstract of DOI:10.1055/s-2008-1078482

A series of 4-substituted 1H-pyrazole-5-carboxylates was prepared from the cyclocondensation reaction of unsymmetrical enaminodiketones [RC(O)C(=CNMe ₂)C(O)CO₂Et, where R = Ph, 4-MeOC₆H ₄, 4-ClC₆H₄, 4-FC₆H₄, 4-O₂NC₆H₄, thien-2-yl, benzofur-2-yl, CCl ₃ and CF₃] with tert-butylhydrazine hydrochloride or carboxymethylhydrazine. The compounds were obtained regiospecifically and in good to excellent yields (73-94%). In addition, 5-carboxyethyl-1-(1,1- dimethylethyl)-1H-pyrazole-4-carboxylic acid was synthesized from regiospecific conversion of ethyl 4-(2,2,2-trichloroacetyl)-1-(1,1-dimethylethyl)- 1H-pyrazole-5-carboxylate. The carbonyl substitution reaction was regiospecific for the trichloroacetyl group and did not affect the ester group. Thieme Stuttgart.