Ethyl halides arene alkylation

Alkylations of arenes by ethyl halides under Friedel-Crafts conditions have been carried out numerous workers. Excellent accounts of the developments made in this area are available from a review, as well as a recent book. Equations (9) to (11) illustrate some ethylation reactions. " ... 

The Heck reaction is a C-C coupling reaction where an unsaturated hydrocarbon or arene halide/triflate/sulfonate reacts with an alkene in presence of a base and Pd(0) catalyst so as to form a substituted alkene. Kaufmann et al. showed that the Heck reaction carried out in presence of ILs such as tetra-alkyl ammonium and phosphonium salts without the phosphine ligands, resulted in high yields of product. They attributed the activity to the stabilizing effect of ammonium and phosphonium salts on Pd(0) species. Carmichael et al. used ionic liquids containing either A,A -dialkylimidazolium and A-alkylpyridinium cations with anions such as halide, hexafluorophosphate or tetrafiuoroborate to carry out reactions of aryl halide and benzoic anhydride with ethyl and butyl acrylates in presence of Pd catalyst. An example of iodobenzene reacting with ethyl acrylate to give trans-et vy cinnamate is shown in Scheme 14. 

Carbon Nucleophiles. Palladium-mediated homocoupling of substituted arenes generally yields mixtures of all possible coupling products. If the reaction is carried out with a catalytic amount of palladium diacetate and with thallium(III) trifluoroacetate as stoichiometric oxidant (eq 67), aryls carrying substituents such as alkyl or halide afford mainly the 4,4 -biaryls in yields ranging from 60% (R = ethyl) to 98% (R = H). Biaryls can also be formed without the palladium catalyst. 

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