The palladium-catalyzed Heck arylation of olefins is one of the most important carbon-carbon bond-forming processes in synthetic organic chemistry. There are at present two main concerns with respect to this reaction: 1) the discovery of catalytic systems that activate the C-Cl bond and 2) the development of phosphane-free palladium catalysts. Chloro-arenes are the most readily available and cheapest starting materials; however, they are generally unreactive under the conditions used to couple the corresponding iodides and bromides. In particular, the use of neutral and electron-rich aryl chlorides requires high temperatures (> 140 °C) as well as expensive and air-sensitive phosphane ligands. A further drawback is that complex substituted olefins (cinnamates or other 1,2-disubstitued alkenes) are relatively uncommon substrates as a result of their low reactivity toward typical catalysts. From a synthetic standpoint, all these factors are considerable limitations that need to be addressed.
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