Cu-Catalyzed Cyanation of Arylboronic Acids with Acetonitrile: A Dual Role of TEMPO.

The cyanation of arylboronic acids by using acetonitrile as the "CN" source has been achieved under a Cu(cat.)/TEMPO system (TEMPO=2,2,6,6-tetramethylpiperidine N-oxide). The broad substrate scope includes a variety of electron-rich and electron-poor arylboronic acids, which react well to give the cyanated products in high to excellent yields. Mechanistic studies reveal that TEMPO-CH2 CN, generated in situ, is an active cyanating reagent, and shows high reactivity for the formation of the CN(-) moiety. Moreover, TEMPO acts as a cheap oxidant to enable the reaction to be catalytic in copper.