An improved protocol for the ruthenium(pybox)-catalyzed asymmetric alkene epoxidation

A considerable rate enhancement in the ruthenium-catalyzed asymmetric epoxidation of olefins in the presence of PhI(OAc)2 is reported. By the addition of H2O, the rate of the reaction was increased by two orders of magnitude. Reactions of both aliphatic and aromatic olefins were realized for the first time and enantioselectivities up to 71% ee were obtained. In addition an in situ generation of ruthenium pybox catalysts for faster screening of oxidation catalysts was also developed.