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

Abstract 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 3 ‐assisted [1,2]‐proton transfer is the enantioselectivity‐determining step.