Nucleophile cyanide

A study of the photo-sensitized ring-opening reactions of the radical cations (76) of arylcyclopropanes (75) with methanol, water, and cyanide nucleophiles suggests a three-electron 5k2 mechanism (Scheme 11).185 The isolated products are methyl propyl ethers, derived from nucleophilic attack of methanol on the radical cation (76). They were detected by UV-VIS spectroscopy and shown to react with nucleophiles by transient kinetic methods. The benzyl radical (77) reacts with the DCB radical anion to afford monoaromatic ether (78) by oxidation and protonation or the disubstituted ether (79) by addition of DCB. Regio- and stereo-selectivity of the substitution were complete regiochemistry and rate constant were profoundly effected by the electronic nature of the aryl substituents.186 Elsewhere, a combined ab initio and CIDNP study... 

Answer The cyanide nucleophile has a p TabH = 9.2 and the bromide leaving group has a p/LaHL of -9. The forward direction drops 18.2 pATa units, so is very favorable. The reverse reaction would have to climb the same 18.2 units, and so is ruled out by our / /(a rule. The reaction goes forward, but is not reversible. 

The Lewis acid-Lewis base bifunctional catalyst 178a, prepared from Ti(Oi-Pr)4 and diol 174 (1 1), realizes highly enantioselective cyanosilylation of a variety of ketones to (R)-cyanohydrin TMS ethers (Scheme 10.241) [645]. The proposed mechanism involves Ti monocyanide complex 178b as the active catalyst this induces reaction of aldehydes with TMSCN by dual activation. Interestingly, the catalyst prepared from Gd(Oi-Pr)3 and 174 (1 2) serves for exclusive formation of (S)-cyanohy-drin TMS ethers [651]. The catalytic activity of the Gd complex is much higher than that of 178a. The results of NMR and ESI-MS analyses indicate that Gd cyanide complex 179 is the active catalyst. It has been proposed that the two Gd cyanide moieties of 179 play different roles - one activates an aldehyde as a Lewis acid and the other reacts with the aldehyde as a cyanide nucleophile. 

Extensive studies on the molybednum complex XXXVI with various bidentate phosphorus and sulfur, ligands demonstrate that hydride, n-butyllithium and cyanide nucleophiles add to the arene to give XXXVII ... 

Note that the cyanide nucleophile introduces both nitrogen and a new carbon. This extra carbon must be accounted for in the retrosynthetic planning. 

Halides can be converted into cyanides. Thus, the reaction of benzyl bromide in toluene with potassium cyanide, catalysed by alumina, on sonication gives the substitution product, viz. benzyl cyanide in 76% yield. In the absence of ultrasound alkylation is the preferred pathway (Scheme 4). The difference is because ultrasound forces cyanide into the surface of alumina, enhancing cyanide nucleophilicity and reducing the lewis acid character. 

Photocyanation of deuterium-labeUed 1-nitronaphthalenes with cyanide nucleophile has been proven to involve primarily an ipso attack followed by isomerizations. The reaction of nucleophiles with halogen-ated aromatics proceeds via attack of the nucleophile on the nitroarene, generating an anionic o-complex. This is followed by departure of the leaving group and rearomatization. Cervera et al. and Huertas et al. have shown a direct coupling of carbon nucleophiles with m-dinitrobenzene via fluoride promoted nucleophilic aromatic substitution (Scheme 5). Amines, amides, ethyl acetate, acetonitrile, and acetone... 

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