Photoredox/Nickel-Cocatalyzed Asymmetric C-O and C-S Couplings for Atroposelective Synthesis of N-Heterobiaryls.

Abstract

Photoredox/nickel-cocatalyzed cross-couplings have emerged as powerful methods for constructing carbon-heteroatom bonds under mild conditions. Despite their rapid development, catalytic asymmetric C(sp2)-heteroatom couplings remain largely underexplored and challenging. Herein, we established photoredox/nickel-cocatalyzed asymmetric C-O and C-S couplings of racemic heterobiaryl triflates with diverse oxygen and sulfur nucleophiles. This straightforward protocol enables highly enantioselective C(sp2)-O and C(sp2)-S bond formation under mild reaction conditions, providing diverse axially chiral N-heterobiaryls (>100 examples) with excellent atroposelectivity and functional group tolerance. These axially chiral N-heterobiaryls can be further transformed into valuable chiral compounds, including commonly used chiral ligands and organocatalysts, while the resultant C-S coupling products can serve directly as chiral ligands in asymmetric catalysis. This study represents the first highly enantioselective photoredox/Ni-cocatalyzed asymmetric C(sp2)-heteroatom bond coupling and introduces a new strategy for atroposelective synthesis of N-heterobiaryl atropisomers with wide applicability. Mechanistic investigations reveal that both C-O and C-S couplings proceed via an energy-transfer pathway: the C-O coupling follows a kinetic resolution mechanism, while the C-S coupling proceeds via dynamic kinetic asymmetric transformation, thus providing valuable insights into this class of C(sp2)-heteroatom couplings and advancing this field.