Cobalt-catalyzed C(sp²)-H/C(sp³)-H coupling via directed C-H activation and 1,5-hydrogen atom transfer

A cobalt-catalyzed C(sp²)-H/C(sp³)-H coupling reaction between an aryl imine and a 2-bromobenzyl-protected secondary amine is reported. Promoted by a combination of a cobalt-N-heterocyclic carbene catalyst and a Grignard reagent, the reaction allows for the introduction of α-aminoalkyl groups into the ortho position of the imine at a mild temperature. The cobalt catalyst is proposed to play key roles in two distinct modes of C-H cleavage, i.e., directed C-H metalation and 1,5-hydrogen atom transfer (HAT).