CHEMISTRY OF OXAZIRIDINES .15. ASYMMETRIC OXIDATIONS USING 3-SUBSTITUTED 1,2-BENZISOTHIAZOLE 1,1-DIOXIDE OXIDES

The synthesis and asymmetric oxidations of chiral nonracemic 3-substituted 1,2-benzisothiazole 1,1-dioxide oxides (6) are described. These new N-sulfonyloxaziridines are prepared by oxidation of the corresponding enantiomerically pure sulfonimines 5. These reagents oxidize sulfides to sulfoxides (11-52% ee), epoxidize nonfunctionalized alkenes (17-61% ee), and oxidize enolates to alpha-hydroxy carbonyl compounds (11-81% ee). Epoxidation of (-)-(S)-limonene with (+)-(2R,3S)-6a, a double asymmetric synthesis, affords a 93:7 cis/trans mixture of limonene oxides. Evaluation of possible transition-state structures suggests that the molecular recognition is primarily determined by steric factors. These reagents are less effective than N-sulfonyloxaziridines 1-3 in their asymmetric oxidations because they lack well-defined regions that are topologically dissimilar near the active site.