How does the Achiral Base Decide the Stereochemical Outcome in the Dynamic Kinetic Resolution of Sulfinyl Chlorides? A Computational Study

The dynamic kinetic resolution of sulfinyl chlorides by addition of the optically active alcohol DAGOH (diacetone D-glucose) in the presence of non-chiral bases was theoretically studied at the ONIOM (Becke3LYP:UFF) level. The dependence of the stereochemical outcome on the nature of the base observed in this reaction was explored considering two electronically similar bases, pyridine and collidine, that are experimentally known to promote opposite diastereoselectivities. Our calculations reproduced the experimental result that the absolute configuration of sulfur in the major reaction product is R with pyridine but S with collidine. The analysis of the optimized geometries revealed that the most sterically active substituent around sulfur is the methyl of the substrate with pyridine but the base itself with collidine. This leads to an inversion of the chiral distribution of steric hindrance around sulfur that induces the reversal of the stereochemical outcome.