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Synthesis 2009(6): 1021-1035  
DOI: 10.1055/s-0028-1087976
PAPER
© Georg Thieme Verlag Stuttgart ˙ New York

Palladium-Catalysed Heck Reactions of Alk-1-en-3-ones with Aryl Bromides: A Very Simple Access to (E)-1-Arylalk-1-en-3-ones

Mhamed Lemhadria, Yacoub Falla, Henri Doucet*b, Maurice Santelli*a
a Laboratoire de Synthèse Organique, Faculté des Sciences de Saint Jérôme, Université d’Aix-Marseille III, Avenue Escadrille Normandie-Niemen, 13397 Marseille Cedex 20, France
Fax: +33(4)91289112; e-Mail: m.santelli@univ-cezanne.fr;
b Institut Sciences Chimiques de Rennes, UMR 6226 CNRS-Université de Rennes 1 ‘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 6 November 2008
Publication Date:
24 February 2009 (online)

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Abstract

When appropriate reaction conditions are used, very high yields of (E)-1-arylalk-1-en-3-one derivatives can be obtained by palladium-catalysed reactions of alk-1-en-3-ones with aryl bromides. The tetraphosphine cis,cis,cis-1,2,3,4-tetrakis(diphenylphosphinomethyl)cyclopentane in combination with [Pd(C3H5)Cl]2 was found to be a very efficient catalyst for this reaction. In general, higher reaction rates were observed with electron-poor aryl bromides, but the electron-rich aryl bromides 1-bromo-4-(dimethylamino)benzene and 4-bromoanisole also led to the arylated enones in high yields. Even with sterically very congested aryl bromides such as 9-bromoanthracene, 1-bromo-2,4,6-trimethylbenzene or 1-bromo-2,4,6-triisopropylbenzene, the expected (E)-1-arylalk-1-en-3-ones were obtained in moderate to good yields. These enones appear to be unstable under the reaction conditions, and the addition of a small amount of hydroquinone to the reaction mixture was found to be crucial, especially for the vinylation of electron-deficient aryl bromides. A variety of alk-1-en-3-ones has been employed, and better results in terms of substrate/catalyst ratios were obtained when oct-1-en-3-one or hex-1-en-3-one was used than when but-1-en-3-one or pent-1-en-3-one was used. It should be noted that several reactions can be performed with as little as 0.1-0.001 mol% catalyst.

Key words

Heck reaction - palladium - catalysis - enones - arylations