Model for the Enantioselectivity of Asymmetric Intramolecular Alkylations by Bis-Quaternized Cinchona Alkaloid-Derived Catalysts

A model for the stereoselectivity
of intramolecular alkylations
by N,N′-disubstituted cinchona
alkaloids reported by Xiang et al. was established using density functional
theory (DFT) calculations. The stereocontrol is based on the minimal
distortion of the transition state (TS) and catalyst required to achieve
favorable electrostatic interactions in the favored TS. Counterions
must be included in computational modeling of ion-paired catalysis
in order to reproduce experimental enantioselectivity.