Ni-catalyzed benzylic β-C(sp)-H bond activation of formamides.

The development of transition metal-catalyzed β-C-H bond activation via highly-strained 4-membered metallacycles has been a formidable task. So far, only scarce examples have been reported to undergo β-C-H bond activation via 4-membered metallacycles, and all of them rely on precious metals. In contrast, earth-abundant and inexpensive 3d transition metal-catalyzed β-C-H bond activation via 4-membered metallacycles still remains an elusive challenge. Herein, we report a phosphine oxide-ligated Ni-Al bimetallic catalyst to activate secondary benzylic C(sp)-H bonds of formamides via 4-membered nickelacycles, providing a series of α,β-unsaturated γ-lactams in up to 97% yield.