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.
在适当的反应条件下,通过
钯催化的alk-1-en-3-ones与芳基
溴化物的反应,可以获得高产率的(E)-1-芳基烯-1-烯-3-酮衍
生物。
铑催化剂中发现四
膦配体顺,顺,顺-1,2,3,4-四(二苯膦甲基)
环戊烷与[Pd(
C3H5)Cl]2结合是一种非常高效的催化剂。通常情况下,电子贫乏的芳基
溴化物显示出更高的反应速率,但电子富集的芳基
溴化物1-
溴-4-(二甲基
氨基)苯和
4-溴苯甲醚也能导致高产率的芳基化烯酮。即使在空间位阻很大的芳基
溴化物如
9-溴蒽、1-
溴-2,4,6-三甲基苯或1-
溴-2,4,6-
三异丙基苯的情况下,期望的(E)-1-芳基烯-1-烯-3-酮也能在中等至良好的产率下获得。这些烯酮在反应条件下似乎是不稳定的,在反应混合物中加入少量的
氢醌被发现是至关重要的,特别是对于电子缺乏的芳基
溴化物的
乙烯基化。已使用了多种alk-1-en-3-ones,当使用辛-1-烯-3-酮或己-1-烯-3-酮时,相对于底物/催化剂比例,得到了更好的结果,而不是丁-1-烯-3-酮或戊-1-烯-3-酮。值得注意的是,有几种反应可以在仅0.1-0.001 mol%催化剂的情况下进行。