Understanding the origin of the enantioselectivity and the mechanism of the asymmetric reduction of ketimine generated from acetophenone with oxazaborolidine catalyst

The enantioselectivity of the oxazaborolidine-catalysed asymmetric reduction reaction of ketimine generated from acetophenone has been investigated by transition state theory at the hydride transfer step using DFT methods at the B3LYP/6-31G(d,p) level of theory. The obtained results indicate that the hydride attack at the Si face is more favourable than the Re one. Analyses of non-covalent interactions and molecular electrostatic potential indicate that the several favourable interactions at the Si hydrogen transfer mode are the origin of the enantioselectivity observed experimentally. Electron Localisation Function topological analysis indicates that the studied hydride transfer step takes place via a non-concerted three-stage mechanism.