Cyanation, aryl halides metal catalyzed

The reaction took place either via the ArSsl or via the AtSn2 mechanism (see Scheme 14.1, paths h,c), and occurred successfully via the first mechanism when using aryl hahdes or esters with electron-donating substituents. Among halides, both aryl chlorides and fluorides underwent photosubstitution when irradiated in an aqueous MeCN solution of KCN (Scheme 14.10, left part) [59]. It should be noted that, in transition metal-catalyzed reactions, the substitution of a chloro- by a cyano-group occurs only under relatively harsh reaction conditions, whereas such a process does not take place at all with aryl fluorides [57]. In the case of aryl esters the photoinduced cyanation occurred conveniently. As esters are easily... 

The exceptional strength of the metal-cyanide linkage makes it challenging to develop catalytic processes that involve excess CN" as reagent. The Pd-catalyzed cyanation of aryl halides discussed in Chapter 19 to form aryl nitriles initially suffered from the formation of catalytically inactive cyanide complexes containing multiple CN" ligands the reaction has been improved by the use of ZnfCN) or Kj[Fe(CN)J as the CN" source. ... 

A Pd-catalyzed cyanation procedure using aryl halides and potassium cyanide was reported in 1973 (Scheme 3.79) [258, 259]. Many studies investigated effective Pd catalysts, metal cyanides, solvents, or additives, intending to provide the efficient catalytic reactions of a variety of carbon electrophiles including aryl halides under rrald conditions. In addition to Zn(CN)2, KCN, and NaCN, several other cyanide sources including NaCN, K4[Fe(CN),5], cyanohydrines, and trimethylsilyl cyanide (TMSCN) have been shown to participate in Pd-catalyzed cyanations [258b]. 

Palladium catalyzed cyanation [71] has recently received a lot of attention in the literature as a cross-coupling which employs cheap, commercially available metal cyanides and incorporates the versatile and synthetically useful cyano group. The development of a domino ort/ o-functionalization/cyanation reaction represents an advance in palladium catalysis as there are very few, if any palladium-catalyzed domino cyanation reactions. The development of the domino ortfto-functionalization/ cyanation [72, 73] by Lautens has led to some of the most significant discoveries of highly functionalized alkyl halides as coupling partners, as well as further development in the selectivity and scope of o/t/to-arylation chemistry. 

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