A useful source of cyanide for the palladium‐catalyzed cyanation of aryl halides is acetone cyanohydrin (see scheme; dpppe=1,5‐bis(diphenylphosphanyl)pentane, tmeda=N,N,N′,N′‐tetramethylethylenediamine). The key to the success of the reaction is the slow dosage of the cyanation reagent to the reaction mixture to prevent the deactivation of the palladium catalyst caused by excess cyanide ions in solution.

The palladium‐catalyzed cyanation of aryl halides is an elegant method for the preparation of benzonitriles. Since its discovery in 1973, this reaction has been the topic of several investigations. Nevertheless, the general methodology is still somewhat underdeveloped compared to other palladium‐catalyzed coupling reactions. Here, we summarize important developments from 1997 until 2003 in this area. Recent contributions from our group include the development of palladium/phosphane/amine catalyst systems for the cyanation of aryl chlorides, the successful cyanation of aryl halides with acetone cyanohydrin and trimethylsilyl cyanide as cyanation reagents, and a general improvement of catalyst efficiency by using a continuous dosage of cyanide sources. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)

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The development of new palladium catalysts for the cyanation of various aryl and heteroaryl chlorides is described. The combination of amine co-catalysts with chelating phosphine ligands, for example, 1,4-bis(diphenylphosphino)butane (dppb) or 1,5-bis(diphenylphosphino)pentane (dpppe), allows an efficient cyanation of chloroarenes with simple potassium cyanide. General palladium-catalyzed cyanation of nonactivated and deactivated chloroarenes is possible for the first time. Studies of the oxidative addition of aryl halides to palladium triphenylphosphine complexes in the presence and absence of amines suggest that the co-catalyst is capable of preventing catalyst deactivation caused by the presence of excess cyanide ions in solution.

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