Low-valent cobalt-catalyzed C–H allylation

An efficient allylation of C–H bonds promoted by a simple cobalt salt combined with a Grignard reagent has been developed. This reaction provides an alternative protocol to the build-up of fundamentally interesting allylated aromatics at room temperature. Mechanistically different from the Cp*Co(III)-promoted transformation, a low-valent cobalt complex that was formed in situ by the reduction with a Grignard reagent can be considered as the catalytically active species, allowing the C–H activation to proceed effectively followed by straightforward coupling with an allylic electrophile to give the product.