Ti(salen)-catalyzed enantioselective sulfoxidation using hydrogen peroxide as a terminal oxidant

(R,R)-Di-μ-oxo Ti(salen) 4 was found to serve as an efficient catalyst for asymmetric oxidation of various sulfides with hydrogen peroxide. For example, oxidation of methyl phenyl sulfide by using 4 as the catalyst in the presence of a urea·H2O2 adduct showed high enantioselectivity of 94% ee. The high enantioselectivity of this reaction was considered to be related to the cis-β-structure of a monomeric Ti(salen) species generated from 4 in a methanol–hydrogen peroxide solution.