Thioether sulfur atoms, metal binding

Major interest has been expressed in the synthesis of chiral sulfoxides since the early 1980s, when it was discovered that chiral sulfoxides are efficient chiral auxiliaries that are able to bring about important asymmetric transformations [22]. Sulfoxides are also constituents of important drugs (e.g., omeprazole (Losec , Priso-lec )) [23]. There is a plethora of routes of access to enantioenriched sulfoxides, and many involve metal-catalyzed asymmetric oxidations [24]. Examples of ruthenium metal-based syntheses of sulfoxides are scarce, presumably due to the tendency of sulfur atoms to bind irreversibly to a ruthenium center. Schenk et al. reported a dia-stereoselective oxidation of Lewis acidic Ru-coordinated thioethers with dimethyl-dioxirane (DMD) (Scheme 10.16) [25[. Coordination of the prochiral thioether to the metal is followed by diastereoselective oxygen transfer from DMD in high yield. The... 

The combination of sulfur and nitrogen donor atoms in crown ethers appears to provide an ideal binding site for Hg + as several sensors, mainly electrochemical, which use azathiacrown ethers to target the metal have been reported. The selectivity for mercury over other metals is often astonishingly high. " A 15-crown-5 C-pivot lariat ether incorporating a thioether side chain was found to extract 46% of Hg + from aqueous solution into dichloroethane, although it was also able to remove almost 100% of Ag+ under the same conditions. ... 

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