Synthesis of Pyrazoles: A Simple, Convenient and Efficient Approach

Pyrazolones are traditionally synthesized by the reaction of -keto esters with hydrazine and its derivatives. To date, synthesis of these compounds have been somewhat limited by the available chemistry. The methods available in literature to synthesize -keto esters are suffers by the use of carbon dioxide and carbon monoxide sources in presence of Pd or transition metal catalysts, long reaction time, use of excess reagent, inconsistent yield, large quantity of by products (due to self Claisen condensation) and require tedious work up procedures to remove the same. Unfortunately the existing methods not produced the -ketoesters of heteroaryl compounds from the heteroaryl esters in good yield. These factors lead us to develop a simple, convenient method to synthesize -keto esters which in turn converted into their corresponding pyrazoles. The synthesis of -oxy/thio substituted -keto esters through cross-Claisen condensation which suffers by many draw-backs, also been improved by new methodology. The newly synthesized compounds were subjected to screen their biological activities and the results discussed.

Autorentext

Associate Professor in Organic Chemistry Division at VIT University, Vellore completed Ph.D at Gandhigram University, Dindigul in Nitrogen Heterocycles. Currently focusing on the synthesis of various heterocycles and exploring their applications in medicinal field; published more than 130 articles in various international journals.

Klappentext

Pyrazolones are traditionally synthesized by the reaction of ß-keto esters with hydrazine and its derivatives. To date, synthesis of these compounds have been somewhat limited by the available chemistry. The methods available in literature to synthesize ß-keto esters are suffers by the use of carbon dioxide and carbon monoxide sources in presence of Pd or transition metal catalysts, long reaction time, use of excess reagent, inconsistent yield, large quantity of by products (due to self Claisen condensation) and require tedious work up procedures to remove the same. Unfortunately the existing methods not produced the ß-ketoesters of heteroaryl compounds from the heteroaryl esters in good yield. These factors lead us to develop a simple, convenient method to synthesize ß-keto esters which in turn converted into their corresponding pyrazoles. The synthesis of a-oxy/thio substituted ß-keto esters through cross-Claisen condensation which suffers by many draw-backs, also been improved by new methodology. The newly synthesized compounds were subjected to screen their biological activities and the results discussed.