Iron/Photosensitizer-Catalyzed Directed C–H Activation Triggered by the Formation of an Iron Metallacycle

C–H functionalization reactions catalyzed by iron, the most abundant transition metallic element in the Earth’s crust, are one of the ideal synthetic methods. However, there are a limited number of strategies for iron-catalyzed directed C–H activation reactions when compared to reactions catalyzed by other first-row transition metals. Here, we report the iron/photosensitizer-catalyzed C–H alkenylation of amide derivatives via a σ-CAM (σ-complex-assisted metathesis) promoted by the in situ generation of an iron metallacycle. Mechanistic experiments suggest that the C–H bond cleavage would proceed via the σ-CAM from a metallacycle generated in situ rather than via the oxidative addition to a low-valent iron species.