Rationalising Diastereoselection in the Dynamic Kinetic Resolution of a -Haloacyl Imidazolidinones

A crossover from SN2 to general base catalysed nucleophilic substitution can account for the dichotomous diastereoselectivity observed in DKR reactions of a-haloacyl imidazolidinones. Aprotic nucleophiles (Nu-) react preferentially with the 5S*,2'R* diastereomer via an SN2 mechanism. Conversely, amines (R2NH) generally react preferentially with the 5S*,2'S* diastereomer. General base catalysis via a bifurcated hydrogen bonded assembly accounts for this anomalous stereoselectivity.