Weak-Chelation Assisted Cobalt-Catalyzed C–H Bond Activation: An Approach Toward Regioselective Ethynylation of N‑Aryl γ‑Lactam

The sustainable C–H bond ethynylation of N-aryl γ-lactam has been achieved in a highly regioselective manner. In this protocol, earth-abundant cobalt(III)-catalyst was found to be effective, triggering the C–H metalation using a weakly coordinating lactam group. Herein, the ortho-(sp2)-H ethynylation has been obtained regioselectively. The mechanistic studies reveal the non-involvement of the radical pathway for this conversion. However, the parallel kinetic isotope experiment suggests that the C–H bond activation is involved in the rate-determining step. In addition, the synthetic utility of ethynylated N-aryl γ-lactam has been demonstrated for many useful transformations.