2- Benzoyl-4-cyanopyridine

A new process for the homolytic acylation of protonated heteroaromatic bases has been developed by Minisci et al. An A-oxyl radical generated from iV-hydroxyphthalimide by oxygen and Co(ll) abstracts a hydrogen atom from an aldehyde. The resulting nucleophilic acyl radical adds to the heterocycle which is then rearomatized via a chain process. Under these conditions, quinoline and benzaldehyde afford three products (Equation 108) <2003JHC325>. A similar reaction with 4-cyanopyridine gives 2-benzoyl-4-cyanopyridine in 96% yield. 

Acyl radicals. Acyl radicals obtained by the oxidation of aldehydes or the oxidative decarboxylation of -keto acids react selectively at the - or -position to the nitrogen of protonated pyridines, quinolines, pyrazines, and quinoxalines, in yields typically in the range 4070% for example, 4-cyanopyridine gives 2-benzoyl-4-cyanopyridine in 96% yield <2003JHC325>. Similarly, pyridines can be carbamoylated in acid media at C(2)/C(4) (Scheme 53). 

More recently Minisci et al. (1986) compared the rate constants for phenylation of 4-cyanopyridine in the 2- and 3-positions by benzenediazonium ions, catalyzed by Cu+ and by Fe2+, with the rates of the same phenylations using benzoyl peroxide under similar conditions. The rate constants found for the phenylation steps were, within experimental error, the same. 

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