Enantiopure p,p’-Disubstituted 1,2-Diphenylethane-1,2-diols as Chiral Inducers in the Ti-mediated Oxidation of Sulfides: a Case of Reversal of Asymmetric Induction by Fluorine Substitution

In the asymmetric oxidation of methyl p-tolyl sulfide, (2a), and benzyl phenyl sulfide (2b) by TBHP, mediated by a titanium complex with enantiopure (R,R)-p,p'-disubstituted-1,2-diphenylethane-1,2-diols, both the unsubstituted diol (R,R)-1a and the p-OMe substituted diol (R,R)-1b lead to sulfoxides of S configuration, with ee up to 99%. On the contrary the p-CF3 substituted ligand (R,R)-1c leads to significantly lower ee and in the case of 2a a reversal of asymmetric induction is observed.