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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
Lemhadri, Mhamed,Fall, Yacoub,Doucet, Henri,Santelli, Maurice
experimental part, p. 1021 - 1035 (2009/12/02)
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. Georg Thieme Verlag Stuttgart.
