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Synthesis 2010(1): 127-135  
DOI: 10.1055/s-0029-1217075
PAPER
© Georg Thieme Verlag Stuttgart ˙ New York

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

Yacoub Falla, Henri Doucet*b, Maurice Santelli*a
a Laboratoire de Synthèse Organique (Equipe Chirosciences, Associée au CNRS, UMR 6263), Faculté des Sciences de Saint Jérôme, Avenue Escadrille Normandie-Niemen, 13397 Marseille Cedex 20, France
e-Mail: m.santelli@univ-cezanne.fr;
b Institut Sciences Chimiques de Rennes, UMR 6226 CNRS-Université de Rennes ‘Catalyse et Organometalliques’, Campus de Beaulieu, 35042 Rennes, France
Fax: +33(2)23236939; e-Mail: henri.doucet@univ-rennes1.fr;
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Publication History

Received 3 September 2009
Publication Date:
22 October 2009 (online)

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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.

Key words

pyrazoles - palladium catalysis - C-H arylation - aryl bromide