Dual role of pyridine N-oxides in ruthenium porphyrin-catalyzed asymmetricepoxidation of olefins

The most important intermediates in the ruthenium porphyrin-catalyzed epoxi dation of olefins by pyridine N-oxides are shown to be N-oxide-coordinated Ru-IV=O complexes. With a chiral ruthenium porphyrin catalyst, the enantios elective epoxidation of terminal aromatic olefins proceeds with up to 80% e e.