Enantioselective Synthesis of “NO₂···NH” Hydrogen Bond-Stabilized C–N Axially Chiral Diarylamines

Abstract

Herein, N -nucleophilic tandem oxidation– N -arylation–oxidation reaction and C -nucleophilic bromination reaction of substituted anilines have been developed using chiral phosphoric acid catalysis, enabling access to axially chiral diarylamines. The key feature of this strategy is that the “NO 2 ···H–N” hydrogen bond was successfully introduced into acyclic diaryl secondary amines, which contain two potential contiguous atropisomeric C–N axes, to stabilize one of the planar axial conformations. This methodology provided a series of optically pure diarylamine atropisomers containing this new hydrogen bond type in good yields (up to 99%) and high enantiomeric ratios (up to 99.5:0.5 e.r.). The synthetic utility was demonstrated through large-scale reactions and transformations of the products. Plausible models were proposed to explain the enantioselectivity of the products.