Conformational enantiodiscrimination for asymmetric construction of atropisomers

Abstract

Molecular conformations induced by the rotation about single bonds play a crucial role in chemical transformations. Revealing the relationship between the conformations of chiral catalysts and the enantiodiscrimination is a formidable challenge due to the great difficulty in isolating the conformers. Herein, we report a chiral catalytic system composed of an achiral catalytically active unit and an axially chiral 1,1′-bi-2-naphthol (BINOL) unit which are connected via a C–O single bond. The two conformers of the catalyst induced by the rotation about the C–O bond, are determined via single-crystal X-ray diffraction and found to respectively lead to the formation of highly important axially chiral 1,1′-binaphthyl-2,2′-diamine (BINAM) and 2-amino-2′-hydroxy-1,1′-binaphthyl (NOBIN) derivatives in high yields (up to 98%), with excellent enantioselectivities (up to 98:2 e.r.) and opposite absolute configurations. The results highlight the importance of conformational dynamics of chiral catalysts in asymmetric catalysis.