Nucleophilic aromatic substitution copper

An extensive series of neutral macrocyclic complexes, mainly of nickel(II), copper(II), platinum(II) and palladium(II), has been developed by Dziomko and coworkers. The cyclization step in the template reaction is a nucleophilic aromatic substitution of an arylamine on to a haloaryl azo compound. A variety of aryl and heteroaryl rings can be incorporated in different combinations. For instance, a diaminoazo compound can be combined with a dihaloazo compound (Scheme 58).246 247 Another synthetic strategy involves the dimerization of an aminohaloazo compound and leads to more symmetrical macrocyclic complexes (Scheme 59).248 249 Most recently, dihalodiazo compounds have been synthesized from dihydrazines and pyrazolinediones and undergo template reactions with simple 1,2-diamines (Scheme 60).249 250... 

Fig. 5.53. Mechanistic aspects I of nucleophilic aromatic substitution reactions of aryldiazonium salts via radicals introduction of Nu=Cl, Br, CN or N02 according to Figure 5.52. Following step 2 there are two alternatives either the copper(II) salt is bound to the aryl radical (step 3) and the compound Ar-Cu(III)NuX decomposes to Cu(I)X and the substitution product Ar-Nu (step 4), or the aryl radical reacts with the cop-per(II) salt in a one-step radical substitution reaction yielding Cu(I)X and the substitution product Ar-Nu.

Side Note 16.2. Figure 16.8 shows a nucleophilic aromatic substitution reaction conducted with copper Rosenmund-von-Braun cyanide. This Rosenmund-von-Braun reaction is not included among the numerous Ull-... 

Copper-mordenite catalyzed nucleophilic aromatic substitution reactions. 

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. 

Paine, A. J. Mechanisms and models for copper mediated nucleophilic aromatic substitution. 2. Single catalytic species from three different oxidation states of copper in an Ullmann synthesis of triarylamines. J. Am. Chem. Soc. 1987,109,1496-1502. 

The mechanism was postulated to involve a Cu(l)-carboxylate as the active species, which promotes oxidative addition of the thioimide. Subsequent transme-talation and C-S reductive elimination generates the thioether product. An excess of boronic acid is often required, as copper catalysts may competitively oxidize aryl substituted boronic acids to the corresponding phenol in the presence of adventitious water [21]. The rate of acceleration observed with amino acids and carboxylate-based ligands, such as 3-methylsalicylate, is attributed to stabilization of a 7i-Cu intermediate generated through a nucleophilic aromatic substitution type mechanism (Scheme 1) [72]. The amino acid or carboxylate ligand may also simply stabilize putative Cu(lll) intermediates. 

One group of nucleophilic aromatic substitution processes does not fit mechanistically into the previous categories. This group is a series of copper-catalyzed displacements of aromatic halogen compounds. 

In all of these reactions, we are using copper salts as the reagents. These reactions are called Sandmeyer reactions. They are useful, because they allow us to achieve transformations that we could not otherwise achieve with the chemistry that we learned in Chapters 3 and 4 (electrophilic and nucleophilic aromatic substitution). As a case in point, we did not see how to install a cyano group on an aromatic ring. This is our first way to do this. 

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