Recent Advances in the Synthesis of Aryl Nitrile Compounds

Aryl nitriles are widely found in natural products, pharmaceuticals, agrochemicals, dyes, and herbicides. Moreover, because the cyano group can be easily converted into various functional groups, aryl nitriles are important intermediates in synthetic organic chemistry. Consequently, the development of new methodologies for the synthesis of aryl nitriles is of significant interest. The traditional methods for their synthesis include Sandmeyer reactions, Rosenmund-von Braun reactions, as well as dehydration reactions of aldoximes and amides. In recent years, numerous efforts have been devoted to transition metal-catalyzed cyanation reactions of aryl (pseudo)halides, organometallic reagents and aryl C-H bonds. A number of cyanating reagents have been explored for such transformations, including metal cyanides and organic cyano group sources. In addition, styrenes and aryl-substituted alkynes are successfully converted into aryl nitriles through carbon-carbon double or triple bond cleavage. Various benzylic compounds have also been used for the synthesis of aryl nitriles, such as benzylic halides, alcohols, amines and azides. Furthermore, the direct conversion of the methyl group of toluene derivatives into a cyano group has also drawn attention. In this critical review, we summarize the recent developments and useful applications in this field and reaction mechanisms are also briefly discussed.