Atroposelective Construction of C─B Axial Chirality via N-Heterocyclic Carbene-Catalyzed Dynamic Kinetic Resolution.

C─B axially chiral architectures are valuable in materials science and medicinal chemistry, but their enantioselective synthesis remains a challenge. Herein, we report an efficient method for the enantioselective synthesis of C─B axially chiral 1,2-azaborines through N-heterocyclic carbene-catalyzed dynamic kinetic resolution. The treatment of racemic 1,2-azaborine-based arylaldehyde with a chiral N-heterocyclic carbene catalyst under oxidative conditions in the presence of an alcohol leads to atroposelective esterification with up to 97% yield and 98% ee. The practicality of this method has been demonstrated by the late-stage functionalization, gram-scale synthesis, and further synthetic transformations. Mechanistic studies indicate that the chiral N-heterocyclic carbene catalyst differentiates between rapidly equilibrating atropoisomeric 1,2-azaborine-based arylaldehyde. DFT studies suggest that the formation of the Breslow intermediate via [Cs]HCO-assisted [1,2]-proton transfer is the enantioselectivity-determining step.