Anisoles, cyanation

Cyanation of iodoarenes with NaCN was catalyzed by [PdCl2(TPPMS)2] in the presence ofNaBH4 and ZnC in water/heptane, toluene or anisole biphasic systems (Scheme 9.11) [37]. Lipophilic catalysts prepared with P(p-tolyl)3 or PPhs showed negligible activities for the biphasic cyanation, due to the lack of CN in the organic phase. The reaction provided good to excellent yields of the respective benzonitriles with several substituted iodoarenes. 

The best conditions for nuclear cyanation involve the use of emulsions, typically CH2Cl2-H20-NaCN, with a phase-transfer agent. This has been described in detail for the monocyanation of naphthalene and anisole with isolated yields in the region 50-70% [222,223]. For dimethoxybenzenes the yields are somewhat lower [223]. 

However, the presence in the anolyte of an anion, which oxidises more readily than the organic substrate and which appears in the substituted product, does not preclude ionisation of the substrate as the operative mechanism. Thus Parker and Burget showed that cyanation of anisole does not proceed at potentials where only cyanide is electroactive ionisation of the anisole is a prerequisite for substitution. " A further example is the chlorination of cyclohexene where, by operating at high electrode potentials at which the olefin is electroactive, chloride ion can be intercepted en route to the anode surface by cyclohexene radical cations diffusing away from it. ... 

Phase transfer agents have been added to organic solutions in order to solubilize salts which comprise supporting electrolytes in electrolytic syntheses [33]. Both naphthalene and anisole were anodically cyanated in dichloromethane according to equation 7.17. The reaction was found to be clean, and high yield, although in both cases, mixtures of positional isomers were isolated. The fact that the reaction was not current efficient was compensated by the inexpensive nature of the supporting electrolyte. 

Photochemical nucleophilic substitutions of aromatic ring systems in protic solvents have been well documented (Scheme 1). When a crown ether is present the photocyanation proceeds better in aprotic solvents than in protic solvents (Scheme 2), while addition of an electron acceptor, such as terephthalonitrile (2), improves both the yields of the photocyanation products and the specificity of substitution (Scheme 3). This report concerns the photochemical cyanation of anisole (1) and dimethoxybenzenes (5) with KCN in an aprotic solvent (CH2CI2), in the presence and absence of 2 when polyethylene glycol (PEG) is present instead of crown ether (CE) (Schemes 4 and 7). 

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