Straightforward and Regiospecific Synthesis of Pyrazole-5-carboxylates from Unsymmetrical Enaminodiketones

Abstract

A series of 4-substituted 1 H-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)-1 H-pyrazole-4-carboxylic acid was synthesized from regiospecific conversion of ethyl 4-(2,2,2-trichloroacetyl)-1-(1,1-dimethylethyl)-1 H-pyrazole-5-carboxylate. The carbonyl substitution reaction was regiospecific for the trichloroacetyl group and did not affect the ester group.