Nickel-catalyzed intermolecular oxidative Heck arylation driven by transfer hydrogenation

The conventional oxidative Heck reaction between aryl boronic acids and alkenes typically involved the Pd II /Pd 0 /Pd II catalytic cycle incorporating an external oxidant and often suffered C=C bond isomerization for internal alkyl-substituted alkenes via chain-walking. Herein, we demonstrate that the regioselectivity (γ-selectivity vs. δ-selectivity) and pathway selectivity (hydroarylation vs. oxidative Heck coupling) of a directed Ni-catalyzed alkene arylation can be controlled by judicious tuning of the coordination environment around the nickel catalyst via optimization of an appropriate phosphine ligand and directing group. In this way, the Ni(0)-catalyzed oxidative Heck arylation that relies on transfer hydrogenation of an acceptor olefin is developed with excellent E / Z selectivity and regioselectivity. Mechanistic investigations suggest that the addition of the acceptor is crucial for lowering the energy for carbometalation and for enabling catalytic turnover. Conventional palladium-catalyzed Heck reactions rely on the addition of oxidants and may suffer from low selectivity. Here, the authors report a nickel-catalyzed oxidative Heck arylation driven by transfer hydrogenation of an acceptor olefin leading to high E/Z selectivity and regioselectivity.