Enantioselective Construction of Quinoxaline-Based Heterobiaryls and P,N-Ligands via Chirality Transfer Strategy
Zeng Gao, Fang Wang, Jinlong Qian, Huameng Yang, Chungu Xia, Jinlong Zhang, Gaoxi Jiang
Abstract
Central-to-axial chirality transfer via C–N single bond oxidation was first achieved as a versatile and conceptually distinct strategy to prepare a new family of axially chiral heteroaromatic biaryl backbones and P,N-ligands (named as Quinoxalinaps) in gram scale. Two atropisomers of Quinoxalinaps (ee >99%) were readily accessed from the same precursor enantiomer by a simple dehydrogenative oxidation with MnO2 and t-BuOOH under mild conditions. Phosphine could be introduced into the ligands before or after the chirality control process. Moreover, these Quinoxalinap P,N-ligands performed well for both asymmetric reactions of the CuBr-catalyzed alkyne conjugate addition with up to −94% ee and AgOAc-catalyzed glycinate imine [3 + 2] annulation with 90% ee, respectively.