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

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)CO(2)Et, where R = Ph, 4-MeOC(6)H(4), 4-ClC(6)H(4), 4-FC(6)H(4), 4-O(2)NC(6)H(4), thien-2-yl, benzofur-2-yl, CCl(3) and CF(3)] 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.