Synthesis of Axially Chiral Phenanthryl-Aryl Phosphines via Nickel-Catalyzed Atroposelective [4 + 2] Cycloaddition...

Axially chiral biaryl phosphines and their oxides are indispensable ligands in asymmetric catalysis, enabling diverse enantioselective transformations. Here, we report the design, synthesis, and applications of a new family of axially chiral phenanthryl-aryl phosphine ligands. We disclose a nickel-catalyzed atroposelective [4 + 2] cycloaddition of biphenylenes with 1-arylalkynes to give axially chiral phenanthryl-aryl bis- and monophosphine oxides, including 2,2'-bis(diphenylphosphine oxide)-1,1'-binaphthy (BINAPO) analogues, as well as monophosphine oxides (MOPOs) and 1-(2-diphenylphosphinyl-1-naphthyl)isoquinoline (QUINAPO) analogues, in high yields and with excellent enantioselectivity. The transformation features 100% atom economy, employs a nonprecious metal, shows broad substrate scope, scales well, and allows easy purification, underscoring strong practical utility. The oxides were readily reduced to the corresponding phenanthryl-aryl MOP- and BINAP-type P(III) ligands. Across multiple representative enantioselective transformations, including hydrogenation, arylation, allylation, and hydrosilylation, these new ligands consistently surpassed benchmark ligands, affording markedly higher enantioselectivity. Density functional theory (DFT) calculations indicate that the cycloaddition-generated phenanthryl unit deepens the chiral pocket around phosphorus, thereby accounting for the high level of stereocontrol.