MECHANISM OF ASYMMETRIC EPOXIDATION .1. KINETICS

The rate of titanium-tartrate-catalyzed asymmetric epoxidation of allylic alcohols is shown to be first-order in substrate and oxidant, and inverse second order in inhibitor alcohol, under pseudo-first conditions in catalyst. The rate is slowed by substitution of electron-withdrawing substituents on the olefin and varies slightly with solvent, CH2Cl2 being the solvent of choice. Asymmetric induction suffers when the size of the alkyl hydroperoxide is reduced. Kinetic resolution of secondary allylic alcohols is shown to be sensitive to the size of the tartrate ester group and insensitive to the steric nature of inhibitor alcohol. Most importantly, the species containing equimolar amounts of Ti and tartrate is shown to be the most active catalyst in the reaction mixture, mediating reaction at much faster rates that titanium tetraalkoxide alone.