A base-assisted metal species modulation mechanism enables Ni-catalyzed stereodivergent transfer semihydrogenation of alkynes with water, delivering both olefinic isomers smoothly using cheap and nontoxic catalysts and additives. Different from most precedents, in which E-alkenes derive from the isomerization of Z-alkene products, the isomers were formed in orthogonal catalytic pathways. Mechanistic studies suggest base as a key early element in modulation of the reaction pathways: by adding different bases, nickel species with disparate valence states could be accessed to initiate two catalytic cycles toward different stereoisomers. The practicability of the method is showcased with nearly 70 examples, including internal and terminal triple bonds, enynes and diynes, affording semi-hydrogenated products in high yields and selectivity.

The β-H elimination, as one of the most important elementary reactions in transition metal chemistry, is a key step in quenching the carbon-palladium bond for the Heck reaction. However, the β-H elimination of the alkenyl palladium species leading to allene is an energetically unfavored process, and therefore, it has been a long-standing challenge in control of this process via enantioselective manner. We developed a concise and efficient methodology to construct trisubstituted chiral allenes from stereodefined fully substituted enol triflates by the enantioselective β - H elimination of the alkenyl palladium species under mild conditions. The identified Xu-Phos play a crucial role in the chemoselectivity and enantioselectivity. Multiple linear regression analysis shows the important steric effect on enantioselectivity. DFT computation results allow us to propose an intramolecular base ( − OAc)–assisted deprotonation mechanism for this progress. Distortion-interaction and energy decomposition analysis indicate that the difference in electrostatic energy ( E elec ) of the two intramolecular base-assisted deprotonation transition states dominates the stereoselectivity.

Recently, the asymmetric bifunctionalization of alkenes has received much attention. However, the development of enantioselective alkoxyalkenylation has posed a considerable challenge and has lagged largely behind. Herein, we report a novel palladium-catalyzed enantioselective alkoxyalkenylation reaction, using a range of primary, secondary and tertiary γ-hydroxy-alkenes with alkenyl halides. By employing newly identified Xu-Phos (Xu8 and Xu9) with a suitable side-arm adjacent to the PCy2 motif, a series of allyl substituted tetrahydrofurans were obtained in good yields with up to 95% ee. Besides (E)-alkenyl halides, (Z)-alkenyl halide was also examined and provided the corresponding cis-product as a single diastereomer, supporting a stereospecific reductive elimination step. Moreover, deuterium labeling and VCD experiments were employed to determine a cis-oxypalladation mechanism, and DFT calculations helped us gain deeper insight into the side-arm effect on the chiral ligand. Finally, the practicability of this method is further demonstrated through a gram-scale synthesis and versatile transformation of the products.