Sulfides chemoselective epoxidation

Sulfides are readily oxidiz by peroxy acids as well as TBHP/Mo. Hence the chemoselective epoxidation of the unsaturated sulfide (183) has been effected by an indirect method the alkene is first trans-... 

In 2002, Ichihara and coworkers reported on the utilization of a Keggin-type phos-phomolybdate (NH4)3PMoi2O40 on apatite as catalyst for the solvent-free epoxidation of olefins (see Section III.A.3.c) and the oxidation of sulfldes and sulfoxides in the presence of urea hydrogen peroxide (Scheme 104) . Chemoselectivities of the oxidation of the sulfides were good [product ratios (sulflde/sulfoxide) 84/16 up to 91/9] depending on the substrate, temperature and reaction time. 

The reaction between sulfur ylides and carbonyl compounds entails attack of the ylide on the carbonyl to form a betaine, which then collapses with expulsion of the neutral sulfide or sulfoxide (Scheme 1 X = R2S ). - - a theoretical study of this mechrmism has appeared. Ylides belonging to the general classes of (1) and (2) differ in stability and in the relative rates of the two mechanistic steps. Specifically, the more stable (2) reacts reversibly with carbonyl groups, whereas (1) undergoes a kinetic addition to the substrate followed by a rapid collapse of the betaine to an epoxide. Differences in chemoselectivity and stereoselectivity between Ae ylides are attributed to this key difference. - - ... 

---