Alkene isomerization-hydroarylation tandem catalysis: Indole c2-alkylation with aryl-substituted alkenes leading to 1,1-diarylalkanes

A cobalt-N-heterocyclic carbene catalyst generated from CoBr₂, imidazolium salt, and cyclohexylmagnesium bromide was found to promote the imine-directed C2-alkylation of indoles with nonconjugated arylalkenes through a tandem alkene isomerization-hydroarylation process, affording 1,1-diarylalkanes with exclusive regioselectivity. The feasibility of the tandem catalysis was demonstrated for allyl-, homoallyl-, and bishomoallylbenzene derivatives. The catalytic system is also applicable to a variety of β-substituted styrene derivatives. Mechanistic experiments using deuterium-labeled indole substrate and Grignard reagent provided insight into the cobalt-mediated C -H activation step, which likely involves exchange of the C2-hydrogen atom of the former and the β-hydrogen atoms of the latter. ...? but thats secondary: A catalytic system consisting of CoBr₂, N-heterocyclic carbene, and cyclohexylmagnesium bromide promotes the imine-directed addition of indoles to nonconjugated aryl-substituted alkenes through tandem alkene isomerization-hydroarylation, affording 1,1-diarylalkane derivatives with exclusive regioselectivity. Deuterium-labeling experiments revealed the involvement of the secondary alkyl Grignard reagent in the cobalt-mediated C -H activation process.