Titanium complexes of chiral amino alcohol derived Schiff bases as efficient catalysts in asymmetric oxidation of prochiral sulfides with hydrogen peroxide as an oxidant

An efficient asymmetric oxidation of prochiral sulfides catalyzed by a series of simple in situ generated complexes based on chiral amino alcohol derived Schiff bases with Ti(Oi-Pr)4 was carried out in presence of cheap and environmentally benign oxidant H2O2 at 0 °C. Prochiral sulfides were converted to respective chiral sulfoxides efficiently (conversion, 93%; up to ee, 98%) with this system in 10 h at 0 °C. The present study demonstrated a significant role of steric influence of the substituent attached on both aryl and alkyl moiety on the enantioselectivity. Kinetic studies of the catalytic reaction showed first order dependence on substrate and catalyst whereas it is zero for the oxidant. Kinetic studies in combination with UV–vis. spectral studies were used to propose a catalytic cycle for the sulfoxidation reaction.

Figure optionsDownload high-quality image (136 K)Download as PowerPoint slideHighlights
► A series of titanium complex were screened for the asymmetric sulfoxidation.
► Factors having influence on the outcome of the reaction was monitored.
► (1S,2R) isomer of the complex found to be more active than the (1R,2S) isomer.
► Substituents on the ligand and substrate greatly affect the result of the reaction.
► Kinetic and UV–vis spectroscopy has been studied to propose a probable mechanism.