Enantioselective oxidation of di-tert-butyl disulfide with a vanadium catalyst:: Progress toward mechanism elucidation

The mechanism of the oxidation of di-tert-butyl disulfide (1) to the chiral thiosulfinate (2) by H2O2 catalyzed by bis(acetylacetonato)oxovanadium and a chiral Schiff-base ligand (3) has been investigated. Techniques included V-51 NMR spectroscopy, solvent effects on reaction enantioselectivity, and the isolation and full characterization of a 2:1 ligand-to-vanadium catalyst precursor. A model for the dramatic solvent effect on the enantioselectivity of this reaction was developed, based on the identification of a competing nonselective oxidation pathway. From this model, strategies for limiting this competing pathway were developed.