Weak-Chelation Assisted Cobalt-Catalyzed C–H Bond Activation: An Approach Toward Regioselective Ethynylation of <i>N</i>‑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.本研究实现了N-芳基γ-内酰胺（N-aryl γ-lactam）的可持续C-H键炔基化（C–H bond ethynylation）反应，且该反应具有优异的区域选择性。在该反应体系中，地壳储量丰富的钴(III)催化剂（earth-abundant cobalt(III)-catalyst）表现出卓越的催化活性，可通过弱配位内酰胺基团触发C-H金属化过程。本研究中，反应可区域选择性地得到邻位(sp²)-H炔基化（ortho-(sp2)-H ethynylation）产物。机理研究表明，该转化过程未涉及自由基路径（radical pathway）。不过，平行动力学同位素实验（parallel kinetic isotope experiment）结果显示，C-H键活化步骤属于该反应的决速步（rate-determining step）。此外，本研究还验证了炔基化N-芳基γ-内酰胺的合成应用价值，该类化合物可参与多种有价值的转化反应。