Nucleophilic aromatic copper catalysis

Nucleophilic aromatic substitutions are a type of reactions frequently applied in the synthesis of chemical intermediates and fine chemicals. In general, these processes are performed in the liquid phase, batchwise, with dissolved copper salts as catalysts [1]. It is of interest to investigate the possibilities of heterogeneous catalysis, as a more convenient catalyst recycle can thus be achieved. 

Direct nucleophilic displacement of halide and sulfonate groups from aromatic rings is difficult, although the reaction can be useful in specific cases. These reactions can occur by either addition-elimination (Section 11.2.2) or elimination-addition (Section 11.2.3). Recently, there has been rapid development of metal ion catalysis, and old methods involving copper salts have been greatly improved. Palladium catalysts for nucleophilic substitutions have been developed and have led to better procedures. These reactions are discussed in Section 11.3. 

A sophisticated chemoselective 1,4-addition of silicon nucleophiles to a.P Unsaturated aldehydes (1,2- versus 1,4-addition) was disclosed by the groups of Ibrahem and Cordova, merging copper(I)-catalyzed silicon-boron bond activation with iminium ion catalysis (Scheme 13) [40]. Proline derivative (S)-68 induced good to high levels of enantiocontrol in reactions of enals with either aromatic [22a-c —> (S)-67a-c] or aliphatic substituents [22d —> (/ )-67d] in the p-position. The chemoselectivity was excellent throughout. Moreover, p,p-disubstituted substrates were also converted chemoselectively with acceptable 76% ee [(S)-69],... 

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