Enhanced Reactivity by Torsional Strain of Cyclic Diaryliodonium in Cu-Catalyzed Enantioselective Ring-Opening Reaction

Summary

Atropisomers are stereoisomers arising from the restricted rotation around a single bond. In particular, biaryl atropisomers represent an important class of compounds, as they are widely present in natural products, ligands and pharmaceutical molecules. However, the preparation of structurally diverse biaryl atropisomers under mild conditions is a significant challenge. Here, we describe a Cu-bis(oxazolinyl)pyridine-catalyzed asymmetric ring-opening amination reaction of cyclic diaryliodoniums. Increasing the torsional strain of these cyclic compounds significantly improved the reactivity of cyclic diaryliodoniums. Computational investigation indicated that the two conformers of the cyclic diaryliodoniums had a low rotational barrier, and generally the reaction achieved high yields and high enantioselectivity (up to >99% ee). Furthermore, this ring-opening amination reaction also featured high atom economy in comparison with traditional reactions involving diaryliodonium. Finally, we propose a catalytic cycle and a mechanistic model that accounts for the observed enantioselectivity.