Aryl halides coupling with cyanides

Aryldiazonium salts, usually obtained from arylamines, undergo replacement of the diazonium group with a variety of nucleophiles to provide advantageous methods for producing aryl halides, cyanides, phenols and arenes by reductive removal of the diazo group. Coupling reaction of aryldiazonium salts with phenols or arylamines give rise to the formation of azo dyes. 

Homogeneous, aqueous tv o-phase catalysis is also of industrial interest for the production of the important intermediate phenylacetic acid (PAA), -which is used in perfume and pesticides syntheses. The previous process (benzyl chloride to benzyl cyanide -with hydrolysis of the latter) suffered from the formation of large amounts of salt (1400 kg per kg of PAA). The new carbonylation method reduces the amount of salt by 60% and makes use of the great cost difference between —CN and —CO [79-81]. Finally, the Suzuki coupling of aryl halides and arylboronic acids, substituting Pd/TPPMS with Pd/TPPTS catalysts, should be also mentioned. 

B.ii.b. Termination by Boronates (Heck-Suzuki Cascade), Stannanes (Heck—Stille Cascade), or Cyanide Ion. The Heck reaction of aryl or alkenyl halides with norbomene can be terminated by coupling with either a boronate (Scheme 5, Eq. or an alkenylstannane (Scheme 5, Eq. 2) to stereoselectively formed vicinal biscoupling products with formation of two new C,C bonds. 

Catalysts containing chelating ligands and conditions that limit the concentration of cyanide have allowed the development of the coupling of cyanide with aryl halides with improved catalyst lifetimes. Recent procedures have been devised that slowly release cyanide from a cyanohydrin or trimethylsilylcyanide or that include less reactive cyanide reagents, such as zinc cyanides. High-yield reactions have also been reported with potassium hexacyanoferrate(II) as a safe cyanide source (Equation 19.19). " This reagent releases little free cyanide, but does transfer cyanide in the catalytic process. It has such little toxicity that it is even used as a food additive. 

This palladium-catalyzed coupling mediated by norbornene has also been conducted with aryl halides containing an ortho substituent in the presence of a coupling partner, such as cyanide (Equation 19.155). In this case, tihe product does not contain the nor-bomene additive. Various coupling partners include cyanide, olefins, allylic alcohols, diphenyl- and alkylphenylacetylenes, arylboronic acids, hydrogen donors, and amides. The proposed mechanism (Scheme 19.20) begins with the oxidative addition of Pd(0)... 

There has been a DFT study of the decarboxylative coupling of cyanoacetate salts with aryl halides. Decarboxylation is likely to be rate determining in the palladium-catalysed formation of a-arylnitriles. The ortho-cyanatioa of arenes carrying a DG by A -cyano-iV-phenyl-p-toluenesulfonamide is catalysed by rhodium. As shown in Scheme 21, the mechanism is likely to involve rate-determining formation of a five-membered rhoda-cycle intermediate, (160), followed by insertion of the cyanide and elimination of a tosylaniline coordinated rhodium complex. ... 

The first such catalytic reaction was reported in 2001 by Miller. Aryl cyanides can be coupled with aryl-, alkyl-, and alkenyl-magnesium halides pretreated with... 

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