Catalytic Asymmetric Oxidation oftert-Butyl Disulfide. Synthesis oftert-Butanesulfinamides,tert-Butyl Sulfoxides, andtert-Butanesulfinimines
The first example of the catalytic asymmetric oxidation of tert -butyl disulfide ( 1 ) is described. The product, tert -butyl tert -butanethiosulfinate ( 2 ) is obtained with 91% enantiomeric excess in yields of ≥92% on scales as large as 1 mol. The application of H 2 O 2 as stoichiometric oxidant in the presence of 0.25 mol % of VO(acac) 2 and 0.26 mol % of a chiral Schiff base ligand, 6a, is both convenient and cost-effective. Thiosulfinate ester 2 is chemically and optically stable and serves as an excellent precursor to chiral tert -butanesulfinyl compounds by the stereospecific nucleophilic displacement of tert -butyl thiolate. Addition of LiNH 2 in liquid ammonia and THF provides tert -butanesulfinamide ( 3; 91% yield). A single recrystallization provides enantiomerically pure 3 in 71−75% overall yield from disulfide 1 . Enantiomerically pure thiosulfinate ester 2 also reacts readily and stereospecifically with Grignard reagents, organolithiums, lithium amides, and lithium imine salts to provide enantiomerically pure chiral sulfoxides, sulfinamides, and sulfinimines in good yield.