Site-Selective sp2 C–H Cyanation of Allenes via Copper-Catalyzed Radical Relay

Compared with the extensively reported hydrogen atom transfer (HAT) at sp3 C–H, abstraction of hydrogen atoms at the sp2 carbon is extremely rare. Here, we communicate the site-selective cyanation of the sp2 C–H bond of allenes using the strategy of copper-catalyzed radical relay. The reactions afford various allenyl nitriles directly from simple allenes with a broad substrate scope and a remarkable functional group compatibility under mild conditions. These reactions exhibit excellent site-selectivity toward sp2 C–H, which can be attributed to the unique pocket created by the Cu-bound nitrogen-centered radical. The favorable HAT on sp2 C–H is due to crucial hydrogen bonding between the fluoride bonded to the Cu­(II) center and the hydrogen atom at the allylic position. These features enable the late-stage functionalization of druglike bioactive molecules containing an allene motif.