Weak‐chelation Assisted Regioselective Indole C(4)‐Alkynylation via Six‐membered Cobaltacycle Intermediate

Abstract Herein a regioselective indole C4‐alkynylation has been uncovered utilizing an earth‐abundant cobalt(III)‐catalyst. For this process, (bromoethynyl)benzene was used as an alkynylating agent. Also, after screening various amide‐protected chelating groups we found dimethyl‐amide is optimal for the in‐situ generation of cobaltacycle intermediate. The six‐membered cobaltacycle intermediate has been detected through high‐resolution mass spectrometry HRMS, which is a key intermediate for this conversion. Further, mechanistic studies were performed such as KIE experiments, and reactions with radical scavengers, and based on the results a plausible mechanism has been proposed. Moreover, to show the application of this methodology, the product has been oxidized to diketone, monoketone, alkene, alkane and further derivatized to a tricycle indole derivative, which is a core structure of many natural products.