Benzonitrile synthesis, pyridine

An unusual final example of a synthesis from pyridines involves the 4-lithiotetra-chloropyridine (128), which with two moles of benzonitrile gave the trichlorodiphenyl-pyrido[3,4- f]pyrimidine (130) via the intermediate (129) (72JCS(P1)2190). The 2-lithio analogue gave the corresponding [3,2-c] derivative. 

Wan and coworkers reported a rhodium-catalyzed [2 -I- 2 + 2] cycloaddition of oximes and diynes for the synthesis of pyridines in 2013 [45]. In their mechanistic study, they exclude the dehydration of oxime to generate the corresponding nitrile followed by the cycloaddition of the nitrile and the alkynes to afford the pyridine as the pathway. As only a trace amount of benzonitrile was produced from oxime under the reaetion conditions. Additionally, pyridine product was detected in less than 20% yield when benzonitrile was subjected to the reaetion with diyne instead of oxime (Scheme 3.19). EtOh was tested as solvent here as well, but not produeed. Later on, they found that by using Rh (NBD)2BF4/MeO-Biphep as the eatalyst system, the reaction can be performed in EtOH [46]. 

Synthesis of Benzonitriles. Arylthallium(III) salts with copper(I) cyanide or copper(II) cyanide afford fair to excellent yields of benzonitriles when heated at reflux in pyridine solvent (eq 24). The use of acetonitrile as solvent gives lower product yields. 

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