Visible‐Light‐Assisted Cobalt‐2‐(hydroxyimino)‐1‐phenylpropan‐1‐one Complex Catalyzed Pd/Cu‐Free Sonogashira–Hagihara Cross‐Coupling Reaction

An effective and inexpensive strategy for the Co(C9H9NO2)3 catalyzed Sonogashira–Hagihara cross‐coupling reaction of aryl bromides containing electron‐rich and electron‐poor substituents with terminal alkynes was demonstrated. The reaction proceeded smoothly in the presence of ethylene glycol as additive and K2CO3 as base in DMF under visible light illumination, and 23 alkyne products were afforded in moderate to excellent yields, including four new diaryl ethynes. Compared with the high‐cost palladium catalyst, cobalt is an inexpensive catalyst with a preponderance of technologized production, and the palladium/copper‐free catalytic system not only provided an efficient process with mild reaction conditions, but also enhanced the substrate group tolerance. Coupling with cobalt: The Co(C9H9NO2)3 complex catalyzed Sonogashira–Hagihara cross‐coupling reaction of aryl bromides with terminal alkynes was demonstrated. Novel diaryl ethynes were afforded in moderate yields under the mild system. Compared with the high‐cost palladium catalyst, cobalt is an inexpensive catalyst with a preponderance of technologized production, and the Pd/Cu‐free catalytic system provided an efficient process and enhanced the substrate group tolerance.