Dehydrative Direct C-H Allylation with Allylic Alcohols under [Cp*CoIII] Catalysis

The unique reactivity of [Cp*Co-III] over [Cp*Rh-III] was demonstrated. A cationic [Cp*Co-III] catalyst promoted direct dehydrative C-H allylation with non-activated allyl alcohols, thus giving C2-allylated indoles, pyrrole, and phenylpyrazole in good yields, while analogous [Cp*Rh-III] catalysts were not effective. The high g-selectivity and C2-selectivity indicated that the reaction proceeded by directing-group-assisted C-H metalation. DFT calculations suggested that the gamma-selective substitution reaction proceeded by C-H metalation and insertion of a C-C double bond, with subsequent beta-hydroxide elimination. The [Cp*Co-III] catalyst favored beta-hydroxide elimination over beta-hydride elimination.