Characterization of a Silver Vinylcarbene Intermediate in Carbene–Alkyne Metathesis and Its Concerted C(sp2)–H Bond Insertion

Herein we present compelling evidence of the intervention of electrophilic silver vinylcarbenes in the carbene-alkyne metathesis (CAM) reaction, leading to a pivotal C(sp2)-H insertion process. The delicate equilibrium between the stability and reactivity of transient species is crucial for efficient detection. Through meticulous mechanistic exploration, we unveil that the mechanism for the C(sp2)-H insertion hinges on the substitution pattern. Indeed, it departs from the previously documented stepwise mechanism (involving Wheland intermediates), and it follows a concerted route, quite uncommon for this transformation.