Iron-catalyzed directed C2-alkylation and alkenylation of indole with vinylarenes and alkynes

Abstract

An iron–N-heterocyclic carbene catalyst generated from an iron(III) salt, an imidazolinium salt, and a Grignard reagent promotes alkylation and alkenylation reactions at the indole C2-position with vinylarenes and internal alkynes, respectively, via imine-directed C–H activation. The former reaction affords 1,1-diarylalkane derivatives with exclusive regioselectivity. Deuterium-labeling experiments suggest that these reactions involve oxidative addition of the C–H bond to the iron center, insertion of the unsaturated bond into the Fe–H bond, and C–C reductive elimination.