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.