Manganese-Catalyzed Asymmetric Transfer Hydrogenation of Heteroatom-Containing Imines and Diarylimines

The efficient synthesis of chiral amines has garnered ongoing interest due to their prevalence in pharmaceuticals and biologically active compounds. However, most existing strategies for their synthesis primarily rely on asymmetric (transfer) hydrogenation (AH/ATH) using noble metal catalysts. Additionally, the AH/ATH of heteroatom-containing imines and diarylimines has posed a longstanding challenge. In this study, we have developed a general method for the ATH of heteroatom-containing imines and diarylimines, catalyzed by a chiral aminobenzimidazole manganese(I) complex, yielding the corresponding amines in up to 99% yield and 99% ee. Furthermore, the reaction proceeds smoothly on a gram scale without any loss of enantioselectivity, indicating its potential applicability in the synthesis of important pharmaceuticals. Based on deuterium labeling and control experiments, we also propose a possible mechanism for this manganese(I)-catalyzed ATH of imines with NH₃·BH₃.