Modeling the stereoselectivity of the beta-amino alcohol-promoted addition of dialkylzinc to aldehydes.

The title reaction has been modeled by a Q2MM force field, allowing for rapid evaluation of several thousand TS conformations. For 10 experimental systems taken from the literature, the pathway leading to the major enantiomer has been identified. Furthermore, several possible contributions to the minor enantiomer have been investigated, providing an identification of the reasons for the sometimes moderate enantioselectivity of the title reaction, and allowing for future rational improvement of existing ligands. The favored pathways to the minor enantiomer, which must be blocked for significant selectivity improvement, differ strongly among ligands. Thus, design ideas are not necessarily transferable between ligand classes, but must be developed for each reaction on the basis of the pathway that needs to be blocked in each specific case. However, we have identified some general structure-selectivity relationships.