Understanding the mechanism and origins of stereoconvergence in nickel-catalyzed hydroarylation of 1,3-dienes with aryl boronates.

Nickel-catalyzed stereoselective hydroarylation is one of the most efficient methods to access functionalized arenes. Herein, computational studies have been applied to reveal the mechanism and origins of ligand-controlled enantioselectivity of Ni-catalyzed hydroarylation of 1,3-dienes using ethanol as the hydrogen source. DFT calculations show that the hydroarylation of ( E )-diene takes place via concerted hydronickelation aided by boronate leading to an alkylnickel(II) intermediate, which further undergoes transmetallation and C-C reductive elimination to deliver the final chiral alkylarene. The hydronickelation is found to be the rate-determining step and is irreversible. The enantioselectivity is dominated by the transmetallation step, in which the ligand-substrate interactions are analyzed to unveil the source of stereocontrol. Besides, mechanistic studies demonstrate that the ( Z )-diene initially reacts to offer a ( S )- Z -alkyl-Ni(II) species, which preferably undergoes facile isomerization via σ-π-σ-π-σ interconversion to the ( R )- E -alkyl-Ni(II) complex rather than the transmetallation step, thus ultimately generating the same ( R )-alkylarene product as ( E )-diene. Overall, the mechanistic understanding will be useful for the further advancement of asymmetric hydroarylation of dienes.