Palladium-Catalyzed Direct Arylation of Pyrazole Derivatives: A Green Access to 4-Arylpyrazoles

Abstract

1,3,5-Trisubstituted pyrazoles were found to be suitable partners for palladium-catalyzed direct arylation via C-H activation/functionalization using aryl bromides. The reaction conditions and the catalyst have a determining influence on the yields. The system using palladium(II) acetate as the catalyst, potassium acetate as the base, and N,N-dimethylacetamide as the solvent promotes selective 4-arylations in moderate to high yields. Several aryl and heteroaryl bromide derivatives have been employed successfully; their electronic properties have a decisive influence on the yields of coupling products. Electron-poor aryl bromides gave satisfactory results, whereas the electron-rich ones gave lower yields.