Mechanism of asymmetric epoxidation. 2. Catalyst structure

Article abstract of DOI:10.1021/ja00001a019

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 of an X-ray structural determination of a titanium tartramide complex reported previously, as analyzed by IR and ¹H, ¹³C, and ¹⁷O NMR spectrometry. The first ¹⁷O 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.