Origin of pi-Facial Stereoselectivity in Nucleophilic Additions. Application of the Exterior Frontier Orbital Extension Model to Imines and Iminium Ions.

Abstract

The experimental data of pi-facial stereoselection of the imines and the iminium ions of cyclohexanone, tropinone, and adamantan-2-ones have been explained by the exterior frontier orbital extension model (EFOE model) previously proposed. In all cases, facial difference in the pi-plane-divided accessible space (PDAS), which represents simple summation of the pi-plane-divided exterior three-dimensional space nearest to the reaction center outside the van der Waals surface, significantly depends on the structure of the imino moieties. In particular the formation of iminium salt significantly affects the magnitude of both the EFOE density and the PDAS values.