Chiral phosphoric acid catalyzed atroposelective C–H amination of arenes: mechanisms, origin and influencing factors of enantioselectivity

Abstract

The amination reaction between azonaphthalene and carbazole to achieve the C–H amination of an arene can be effectively accomplished by the usage of a chiral phosphoric acid catalyst, which can generate the important N-arylcarbazole framework compound with high yield and excellent enantioselectivity. To figure out the reaction mechanism, origin and influencing factors of enantioselectivity, quantum mechanical calculations were carried out. The results indicate that two pathways lead to the experimental desired major product while other two pathways lead to the enantiomeric minor product. The theoretical ee value is 90% which is in agreement with the experimental 96% ee value. Quantum theory of atoms in molecules was employed to illustrate the roles of weak intermolecular interactions in the reaction process. A detailed analysis of the types of chiral phosphoric acids was performed to elaborate on what factors affect the enantioselectivity and how they cause the effect, and a statistical analysis of the performances of different types of chiral phosphoric acids in the C–N and C–C bond formation reactions was conducted. It is expected that the present work would be insightful for understanding the chiral phosphoric acid catalyzed C–N cross-coupling reaction and thus can guide the selection of chiral phosphoric acids for the asymmetry reaction.