Sharpless epoxidation give just one nearly pure enantiomer of the product because of the chiralty of the diethyl tartrate.
Work Step by Step
When the chiral diethyl L-tartrate, forms a complex with titanium(IV) isopropoxide, the complex is also chiral. The alkene reaction between alkene and tert-butyl hydroperoxide occurs on one face of the alkene causing the formation of one epoxide stereoisomer. Without the chiral chiral diethyl L-tartrate, there is a formation of racemic products.