Origin of pi-facial stereoselectivity in nucleophilic additions. Application of the exterior frontier orbital extension model to imines and iminium ions

The experimental data of pi-facial stereoselection of the imines and the im inium ions of cyclohexanone, tropinone, and adamantan-2-ones have been expl ained by the exterior frontier orbital extension model (EFOE model) previou sly proposed. In all cases, facial difference in the pi-plane-divided acces sible space (PDAS), which represents simple summation of the pi-plane-divid ed exterior three-dimensional space nearest to the reaction center outside the van der Waals surface, significantly depends on the structure of the im ino moieties. In particular the formation of iminium salt significantly aff ects the magnitude of both the EFOE density and the PDAS values.