Disulfides, diphenyl sulfoxide

The proposed mechanism of the oxidative cleavage of S-protecting groups by the chlorosilane/sulfoxide procedure is outlined in Scheme 8. 95 The first reaction is considered to be formation of the sulfonium cation 9 from diphenyl sulfoxide (7) and the oxygenophilic silyl compound 8. The formation of a sulfonium ion of this type is known and has been utilized for the reduction of sulfoxides. 97 Subsequent electrophilic attack of 9 on the sulfur atom of the S-protected cysteine residue leads to the formation of intermediate 10, whereby the nature of the silyl chloride employed should be the main factor that influences the electrophilicity of 9. The postulated intermediate 10 may then act as the electrophile and react with another S-protected cysteine residue to generate the disulfide 11 and the inert byproduct diphenyl sulfide (12). This final step is analogous to the reaction of a sulfenyl iodide as discussed in Section 6.1.1.2.1. 

The first report of the photochemistry of a conjugated aromatic sulfoxide appears to be that of Kharasch and Khodair [32]. In a study more principally aimed at the sulfones, they showed that photolysis of diphenyl sulfoxide 5-H in benzene led to biphenyl 41 (53%), diphenyl sulfide (7%), and trace diphenyl-disulfide 45. Biphenyl was also the major product of diphenyl sulfone photolysis, and it was shown to arise from attack of the photochemically generated phenyl radical on solvent (benzene). The same mechanism was clearly implied for the sulfoxide. The disulfide presumably comes from secondary photolysis of the unobserved phenyl benzenesulfenate 42. (The formation of the sulfide is addressed below in the section of deoxygenation.) Later workers showed that pyridine could be tolylated by photolysis of di-p-tolyl sulfoxide 5-Me with a product distribution quite consistent with other radical phenylations [33]. 

MeSiCl3 has been found useful as a deprotecting agent in peptide chemistry. It also promotes, in conjunction with diphenyl sulfoxide, formation of disulfide bonds in peptides (eq 12). ... 

The photochemical behavior of a number of substituted derivatives of thiochroman-4-one 1-oxides has been examined by Still and coworkers192-194. These authors also report that rearrangement to cyclic sulfenates, with subsequent reaction by homolysis of the S—O bond, appears to be a particularly favorable process. For example, ultraviolet irradiation of a solution of 8-methylthiochroman-4-one 1-oxide (133) in benzene for 24h afforded a single crystalline product which was assigned the disulfide structure 134 (equation 54). More recently, Kobayashi and Mutai195 have also suggested a sulfoxide-sulfenate rearrangement for the photochemical conversion of 2,5-diphenyl-l,4-dithiin 1-oxide (135) to the 1,3-dithiole derivatives 136 and 137 (equation 55). 

Cram (98) using nitrosyl hexafluorophosphate or nitrous acid. Oae and his group (99) also have reported a method for the stereospecific deimination of 60 by means of elemental sulfur or diphenyl disulfide at 160°C. All these procedures give chiral sulfoxide with the same configuration at sulfur as that of the starting sulfoximides 60. 

Since the oxidative polymerization of diphenyl disulfide catalyzed by VO(acac)2 results in selective formation of thioether bonds without any oxygenated compounds such as sulfoxides and/or sulfones, it should be noted that H20 should be produced predominantly by the reduction of 02 catalyzed by the vanadium complex without the formation of partially reduced side products such as H202. 

Similarly, the /ra r-3-substituted-4-sulfenyl /3-sultams 126 can be synthesized as major products by treatment of 3-substituted /3-sultams with LDA followed by reaction with diphenyl disulfide. These are accompanied by the 3,4-air-isomers 127. It should be noted that these air-isomers can be converted to the trans-isomers by treatment with LDA in tetrahydrofuran (THF) at — 78 °C. Oxidation with /-chloroperbenzoic acid (MCPBA) provides /ra r-3-substituted-4-sulfinyl /3-sultams 128 as mixtures of stereoisomers at the sulfoxide moiety. This strategy was applied to obtain chiral 3-substituted-4-sulfinyl /3-sultams with a high diastereoselectivity (Scheme 38) <1998JOC8355>. 

MILD AND SELECTIVE OXIDATION OF SULFUR COMPOUNDS IN TRIFLUOROETHANOL DIPHENYL DISULFIDE AND METHYL PHENYL SULFOXIDE... 

Methods of preparation. Diphenyl disulfide can be prepared by the action of hydrogen peroxide in acidic or basic media, iodine-hydrogen iodide, Sm/BiCl3 in water,"" FeCl3/Nal"" , and by using bromine-aqueous potassium hydrogen carbonate." Methyl phenyl sulfoxide has also been prepared from thioanisole by the action of hydrogen peroxide in methanol, mCPBA, " peroxytrifluoroacetic acid and sodium periodate. ... 

The reaction of enolates with dimethyl disulfides (MeSSMe) or diphenyl disulfides (PhSSPh) leads to the corresponding sulfides. Their oxidation to sulfoxides followed by heating provides a route to functionally substituted alkenes, such as a,[3-unsaturated carbonyl compounds. In the example below, the exocyclic alkene is formed since that is the only possible yn-elimination product. 

Oxygen transfer to sulfur, which leads to sulfoxides and/or sulfones are displayed in Scheme 6. Excess dioxirane converts bis-thiophenylmethane into its bis-sulfone [23] 29 quantitatively. When using stoichiometric amounts of dioxirane, thioenol ethers are transformed into their sulfoxides [23] 30, but excess dioxirane leads to the sulfone [23] 31. As expected, the thioisoflavone [24] 32, the allene sulfoxide [25] 33, and the bis-methylthiobutadiene [26] 34 gave the corresponding sulfones even when excess dioxirane was employed. Of potential synthetic value is the direct oxidation of thioesters to oxo sulfones [27] 35. Finally, diphenyl disulfide afforded the S-thiosulfinate [23] 36 as major product when dioxirane was used in stoichiometric quantity. 

Thiophenol is oxidized with DCT or TBT to diphenyl disulfide. The latter reacts with DCT under more rigid conditions to give benzyl chloride. DCT oxidizes dibenzyl sulfide in methanol to dibenzyl sulfoxide (69ZC325) (Scheme 120). 

Pogonowski have described a route to 5-alkyl-A -cyclopentenones from cyclo-pentanone, the first step of which is sulfenylation with diphenyl disulfide and LDA followed by periodate oxidation to the jS-keto sulfoxide (1). This product is converted into the dianion with 2 eq. of lithium diisopropylamide the dianion... 

The sulfoxide is prepared by treatment of diphenyl disulfide with vinyllithium followed by peracid oxidation. 

Pyrrole and 1-methylpyrrole can be sulfinylated by sulfinyl chlorides or A-(phenyl-sulfinyl)succinimide. The products are prone to rearrange to the 3-isomers on contact with acid <80JOC5336>. A phenylsulfinyl group has been introduced at C3 of the indole ring by 3-sulfenylation of AT-lithioindole with diphenyl disulfide, followed by A-sulfonylation and oxidation to the sulfoxide <89JOCi782>. Sulfenylindoles can be oxidized to sulfones by MCPBA <93JMC1425>. 

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