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4-Arylation of 3-alkoxypyrazoles

Abstract : Following the study of the alkoxypyrazoles nitrogen's reactivity toward arylation or alkylation reactions, we report here our results on the introduction of various aryl groups on carbon 4 position of 3-alkoxy pyrazoles. This was achieved from the corresponding 4-halogeno derivatives via a Suzuki-Miyaura aryl- aryl coupling reaction. The unexpected difficulties (lack of reactivity or unwanted halogen reduction) encountered in the C-4 arylation of NH-free 4-halogenopyrazoles led us to design solutions to this recurrent problem. The cleavage of the 3-alkoxy group was also investigated using hydrogen bromide in acetic acid or boron tribromide in dichloromethane. This led, in one case, to the observation of a remarkable neighboring group-assisted electrophilic aryl boronylation. This second part of our work paves the way to the synthesis of many original chemical libraries featuring 3-alkoxy 1,4-diaryl pyrazoles as well as the corresponding 1,4-diaryl pyrazol-3-ones
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https://hal-pasteur.archives-ouvertes.fr/pasteur-00370362
Contributor : Yves Janin <>
Submitted on : Tuesday, March 24, 2009 - 11:10:09 AM
Last modification on : Monday, June 22, 2020 - 12:08:07 PM

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Sandrine Guillou, Olivier Nesmes, Mikhail Ermolenko, Yves L. Janin. 4-Arylation of 3-alkoxypyrazoles. Tetrahedron, Elsevier, 2009, 65, pp.3529-3535. ⟨10.1016/j.tet.2009.01.109⟩. ⟨pasteur-00370362⟩

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