Catalytic asymmetric oxidation of tert-butyl disulfide.: Synthesis of tert-butanesulfinamides, tert-butyl sulfoxides, and tert-butanesulfinimines

The first example of the catalytic asymmetric oxidation of tert-butyl disulfide (1) is described. The product, rert-butyl tert-butanethiosulfinate (2) is obtained with 91% enantiomeric excess in yields of greater than or equal to 92% on scales as large as 1 mel. The application of H2O2 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 LiNH2 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.