Site-Selective sp 2 C-H Cyanation of Allenes via Copper-Catalyzed Radical Relay.

Compared with the extensively reported hydrogen atom transfer (HAT) at sp 3 C-H, abstraction of hydrogen atoms at the sp 2 carbon is extremely rare. Here, we communicate the site-selective cyanation of the sp 2 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 sp 2 C-H, which can be attributed to the unique pocket created by the Cu-bound nitrogen-centered radical. The favorable HAT on sp 2 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.