A study of factors affecting enantioselectivity in the oxidation of aryl benzyl sulfides in the presence of chiral titanium catalysts

A series of experiments was performed to test a theoretical model that we have recently proposed to explain the highly enantioselective oxidation of aryl benzyl sulfides with tert-butyl hydroperoxide in the presence of a complex between titanium and (S,S)- or (R,R)-hydrobenzoin. The studied variations involved the sulfides, the ligands, and the order of addition of reactants. The reaction path predicted by our model was confirmed in every experiment. In particular, aryl benzyl sulfides behaved as the ideal substrate for this type of asymmetric oxidation, which yields synthetically useful, enantiopure aryl benzyl sulfoxides in a straightforward manner. The theoretical model of the enantioselective oxidation of aryl benzyl sulfides in the presence of chiral titanium catalysts was tested with a series of experiments in which the reagents and conditions were varied. It was confirmed that aryl benzyl sulfides are an ideal substrate for this oxidation protocol, which yields the synthetically useful chiral non-racemic aryl benzyl sulfoxides. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.