Mechanism of asymmetric epoxidation. 2. Catalyst structure

The dominant species in equimolar mixtures of titanium tetraalkoxides and dialkyl tartrate esters is shown to be [Ti(tartrate)(OR) 2 ] 2 , which is identified as the active catalyst for asymmetric epoxidation of allylic alcohols by tertiary alkyl hydroperoxides. The solution-phase structure of this species is consistent with the results on an X-ray structural determination of a titanium tartramide complex reported previously, as analyzed by IR and 1 H, 13 C, and 17 O NMR spectrometry. The first 17 O NMR spectra of titanium (IV) alkoxide and alkyl peroxide complexes are reported, as well as the results of a secondary deuterium isotope effect study on the asymmetric epoxidation reaction. General conclusions concerning the mechanism of asymmetric epoxidation are presented