Direct coupling, aryl halides with enolates

Enolate Arylation Reactions. The direct coupling of aryl halides with enolates (or enolate equivalents) of ketones, esters, and amides is now well established. Malonic esters, cyanoacetates, and malononitrile can be arylated upon treatment with aryl halides in the presence of Pd(dba)2 and electron-rich phosphines or N-heterocyclic carbenes. Carbene ligands have also proven effective in promoting the a-arylation of protected amino acids. As a caveat to the use of Pd(dba)2, the arylation of azlactones in the presence of this palladium source and phosphines was less efficient than that with Pd(OAc)2. The dba ligands were found to react with azlactone substrates to form catalytically inactive palladium complexes. Diastereoselective enolate arylation has been achieved through the use of chiral auxiliaries appended to preformed enol silyl ethers (eq 23). The role of the zinc additive is not clear, however, it appears that discrete zinc enolates are not involved. 

The described procedures are easy to carry out even at multi-gram scale and do not require complicated handling. The scope of the reactions are also quite broad since a wide range of aryl halides with different functional groups can be efficiently coupled. Furthermore, the Heck arylation conditions are mild, using only a weak base (potassium carbonate) and moderate reaction temperatures. Alternative methods for the preparation of triarylated ketones and diarylated aldehydes,[8] are mainly those which relies on direct palladium-catalysed coupling of carbon nucleophiles (enolates) with aryl halides in the presence of a strong base.[9-12]... 

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