Oxygen dialkyl sulfoxides

A series of [3-carbonyl sulfides was studied as substrates for CPO-catalyzed oxygenation (Scheme 2.16) [238]. The corresponding dialkyl sulfoxides formed quantitatively if R2 is methyl or ethyl, but the yields drop dramatically for larger substituents. The steric control was present also in cyclic derivatives where the cyclohexanone residue results in about a 50% reduction in yield with respect to the smaller cyclopentanone. Surprisingly, the y-butyrolactone produces the sulfoxide in quantitative amounts [239]. A similar result was obtained with benzo[fo]thiophenes as substrates [240]. 

The main methodologies developed until now for enantioselective oxidation of sulfides are effective only in the oxidation of alkyl aryl sulfoxides. Dialkyl sulfoxides on the other hand are generally oxidized with only poor selectivity. In an attempt to solve this problem, Schenk s group69 recently reported a stereoselective oxidation of metal-coordinated thioethers with DMD. The prochiral thioether is first coordinated to a chiral ruthenium complex by reaction with the chloride complexes [CpRu[(S,S)-chiraphos]Cl], 36. Diastereoselective oxygen transfer from DMD produces the corresponding sulfoxides in high yield and selectivity. The chiral sulfoxides 37 are liberated from the complexes by treatment with sodium iodide. Several o.p. aryl methyl sulfoxides have been obtained by this method in moderate to high ee (Scheme 12). 

Fluorinated and Ghlorfluorinated Sulfonic Acids. The synthesis of chlorinated and fluorinated sulfonic acids has been extensively reviewed (91,92). The Hterature discusses the reaction of dialkyl sulfides and disulfides, sulfoxides and sulfones, alkanesulfonyl haHdes, alkanesulfonic acids and alkanethiols with oxygen, hydrogen chloride, hydrogen fluoride, and oxygen—chloride—hydrogen fluoride mixtures over metal haHde catalysts, such as... 

Disulfides (73) are oxidised by hydrogen peroxide to the corresponding sulfenic acids (45) dialkyl disulfides may also be converted to thiol sulfinates by treatment with perbenzoic acid thus, diallyl disulfide (71) yields allicin (72), an essential component of garlic (Scheme 55). The latter reaction involves a nucleophilic attack of the sulfur atom on the oxygen of the peroxide group, and therefore the more electron-rich sulfur atom is preferentially oxidised. For instance, methyl phenyl disulfide (85) yields the sulfoxide (86) (Scheme 56). 

Singlet oxygen reactions. Dialkyl sulfides are oxidized to sulfoxides by singlet oxygen. Diphenyl sulfide is practically inert under the same conditions. However, if it is added to the photooxidation of a dialkyl sulfide, it is converted into diphenyl sulfoxide. The interpretation advanced by Foote and Peters is that diphenyl sulfide reacts readily with persulfoxides, formed in the reaction of alkyl sulfides with singlet oxygen ... 

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