Enantioselective oxidation of sulphides to sulphoxides in the presence of bovine serum albumin

In situ generated dioxiranes oxidize a series of prochiral sulphides to the corresponding sulphoxides with enantiomeric excess (e.e.) up to 89%, when bovine serum albumin (BSA) is used as chiral auxiliary. The degree of enantioselectivity, as well as yield and reaction times, depend upon the nature of the dioxirane. These are compared with enantioselectivities attainable for the same transformations by using peroxomonosulfate alone, i.e. in the absence of ketone. In the oxidation of prochiral keto sulphides (wherein the carbonyl functionality serves as precursor of dioxirane) with peroxomonosulfate, optically active keto sulphoxides are isolated in satisfactory chemical and optical yield (up to e.e. 84%).