Arenes, oxidation cyanation

Recyclable [bis(trifluoroacetoxy)iodo]arenes 66 and 70 are excellent reagents for oxidative coupling of thiophenes or pyrroles [79] and for direct oxidative cyanation of heteroaromatic compounds using Me3SiCN as source of cyanide anion [80,81]. 

There have been several recent investigations into the mechanism of photo-cyanation of aromatic hydrocarbons. The process with naphthalene, biphenyl, and phenanthrene has been subjected to a kinetic analysis the reactions in dry or aqueous methyl cyanide are shown to involve two transient species, the first of which is an ionic complex formed from a triplet excimer of the arene, or, in the presence of an electron acceptor, from a triplet exciplex. Reaction of the transient complex with the cyanide ion yields the radical ArHCN, and in aqueous methyl cyanide this second transient reacts with itself to produce dihydrocyano- and cyano-compounds. In dry methyl cyanide the radical species is oxidized to the cyano product. 

More recently, Jin et al. discovered an efficient copper-catalyzed cyanation of arenes 119 nsing benzyl nitrile as a cyanide anion surrogate, which fiunishes aromatic nitriles 120 (Scheme 5.84) [85]. The process involves at least three steps, where (1) benzyl nitrile undergoes a copper-catalyzed oxidation with air to generate A and B, accompanied by the generation of Cu(II) species (2) cyanide anion is formed throngh a retro-cyanohydrination of A or/and hydrolysis of B and (3) the in situ-generated cyanide anion participates in the copper(II)-catalyzed aerobic oxidative C—H fnnctionalization to afford the cyanation product. 

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