Protonation Behavior of 1,1′-Bi-2-naphthol and Insights into Its Acid-Catalyzed Atropisomerization

The behavior of 1,1′-bi-2-naphthol (BINOL) in variety of (super)­acid media has been studied by NMR. The results are combined with the theoretical (DFT) study of the role of mono- and diprotonated forms of BINOL in the acid-catalyzed atropisomerization of this compound. It is demonstrated that the process of enantiomeric configuration exchange proceeds mainly via internal rotation around the C1­(sp³)–C1′(sp³) bond in intermediates such as C1-monoprotonated keto or C1,C1′-diprotonated forms of BINOL, depending on the acidity level