Grignard reagents, the Kharasch reaction

Cross-coupling reactions of aryl halides and sulfonates with organolithium and Grignard reagents, the Kharasch reaction 

The latter is known as the elimination-addition mechanism of the nucleophilic aromatic substitution. The high reactivity of aryllithiums precludes the use of several types of functional groups such as aldehydes, ketones, esters, amides, amines, alcohols, phenols, nitro-compounds, carboxylic acids etc. However, properly protected alcohols, phenols or amines can effect the reaction. Various ether protecting groups, e.g. Tr, Me, /-Pr, Bn, 4-MeOBn, are employed in the former instances, whereas A, V-dibenzyl group is convenient for the amine protection. 

Nevertheless, the cross-coupling reactions of simple aryl- or heteroaryl-lithiums have been efficiently accomplished with aryl iodides and bromides bearing no above-mentioned sensitive groups. The aryllithiums are prepared under an inert atmosphere of argon (nitrogen is not completely inert to ArLi) by the following alternative reactions [13]  

Despite the stoichiometric requirements of expensive palladium salts, this reaction can be useful in the synthesis of ortho-foxmy -, A,A-dialkylaminomethyl-, and amino-substituted biaryls since variuos nitrogen containing substrates at benzylic position readily form palladacycles, e.g. A,A-dimethylbenzylamine, A-benzylidene-A ,A -dimethylhydrazone, O-methylbenzaldoximes, and A-acylanilines [17,18]. 

The Grignard reagents are far more applicable counterparts in the nickel- and palladium-catalysed Kharasch cross-coupling reactions with aryl halides (1, Br, Cl), as well as aryl triflatcs, to give biaryls in moderate to excellent yields [19]. In early 

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