Diaryl sulfides, oxidation

The final products of oxidation of diarylselenides and tellurides (and sulfides as well) in the presence of nucleophiles are the corresponding chalcogen (IV) compounds. In the presence of water, the selenoxide or telluroxide (or the corresponding dihydroxy selenane or tellurane) is the final product. This still leaves several possible pathways, leveraged from early mechanistic studies done using electrochemical techniques on diaryl sulfides and outlined by Engman (Fig. 32). In these pathways, the initial radical cation can react with a nucleophile present in solution, or the dication resulting from further oxidation or disproportionation can do so. 

It has been shown that a phase-transfer catalyst could control the oxidation of sulfide to the corresponding sulfoxide. Thus, the oxidation of diaryl sulfides to sulfoxides using Oxone and PTC (equation 54) is in contrast with the reaction in polar solvents without PTC which gives sulfones as a major product. 

Various alkyl aryl and diaryl sulfides were oxidized selectively to the corresponding sulfoxides in high yields as the major products using sulfonylperoxy intermediate 51 (equation 86) ". ... 

Oxidation of diaryl u fidesJ Ceric ammonium nitrate oxidizes diaryl sulfides in high yield to the corresponding sulfoxides without ovcroxidalion to sulfoncs. The... 

Oxidation of elemental sulfur and selenium with SbFs leads to the formation of doubly charged polyatomic cations [26]. These cations can react with polyfluorinated arenes to form diaryl sulfides or selenides (Eq. 12) [27]. 

Trifluoromethylated sulfenimines which are useful starting materials for the preparation of A(-fluoroalkylamines, aminoketones and aminoalkanoates, have been prepared by the anodic oxidation of 2,2,2-trifluoroethylamine and diaryl sulfides in MeCN/Et4NC104 with MgBr2 as the redox mediator (Scheme 49) [276]. 

Low-valent nickel species catalyze the reaction between Grignard reagents and aryl or alkenyl sulfide in the preparation of alkylarenes, biaryls, and alkenes (see citations in Ref. ///). Wenkert et al. recently isolated compounds 132 and 133 to show that an oxidative addition occurs between diaryl sulfides and tris(tri-/ -butyl)phosphinonickel (77/). 

N03)j, a newcomer to the arena of oxidants, is useful for the acetoxylation of aromatic side chains in benzylic positions [415, 416] and for the oxidation of methylene or methyl groups that are adjacent to aromatic rings to carbonyl groups [238, 415, 417]. The reagent also oxidizes alcohols to aldehydes [418, 419, 420, 421] and phenols to quinones [422, 423], cleaves vicinal diols to ketones and a-hydroxy ketones to acids [424, 425], and converts diaryl sulfides into sulfoxides [426]. A specialty of ammonium cerium nitrate is the oxidative recovery of carbonyl compounds from their oximes and semicarbazones [422, 427] and of carboxylic acids from their hydrazides [428] under mild conditions. 

Dialkyl sulfides, alkyl aryl sulfides, diaryl sulfides, and cyclic sulfides are oxidized to the corresponding sulfoxides or sulfones. Often, both products can be obtained on oxidation with the same oxidant, depending on... 

Sulfide oxidation. Sulfides can be oxidized to sulfoxides in anhydrous methanol as solvent with 1 equiv. of either N-chlorosuccinimide or N-bromosuccinimide in 65-93% yield. In the case of diaryl sulfides the oxidation can be controlled to give either the sulfoxide or the sulfone.5... 

Furthermore, the thianthrene 5-oxides (57), substituted or not, react with n-butyllithium or phenyllithium to provide various dibenzothiophene derivatives (58) and diaryl sulfides (59) (Equation (7)) <91H(32)675>. 

Diphenyl sulfide undergoes disulfonation very rapidly without being able to form the cation radical, while other diaryl sulfides give only low concentrations of cation radical (Shine et al., 1967). Fortunately, these problems can be avoided by using other oxidizing systems such as aluminum chloride-nitromethane solutions. 

Reversible C-S bond cleavage of diaryl sulfide is known. Treatment of Ni(cod)2 with phenyl p-tolyl sulfide in the presence of PEt3 results in the C-S bond cleavage at room temperature, giving a mixture of h a 5-(benzenethiolato)(/5-tolyl)nickel(II) and trans-(phenyl)(/ -toluenethiolato)nickel(II) (Eq. 3.37) [146]. Heating of the reaction mixture leads to the equilibration suggesting reversible oxidative addition/reductive elimination (Scheme 3.77). 

The partial oxidation of sulfides to sulfoxides has been accomplished in a few cases by careful control of the reaction stoichiometry and conditions. A biphasic procedure for sulfoxide formation from diaryl sulfides is shown in eq 23. However, a more attractive and versatile procedure uses a solid Oxone-wet alumina reagent with a solution of the sulfide. This method permits control of the reaction to form either the sulfoxide or the sulfone simply by adjusting the amount of oxidant and the reaction temperature, as illustrated in eq 24. These oxidations are compatible with other functionality. 

Diaryl sulfides are nicely oxidized at room temperature by CAN into... 

Diels-Alder reaction of alkynyl sulfides followed by oxidation has been used for the synthesis of diaryl sulfides (Scheme 16.22) [23]. 

Alkylaryl and diaryl sulfides do not react with the /rani -dioxo species presumably because of their decreased nucleophilicity. Of note, an Fe(TPP)Cl/PhIO system effects oxidation of dialkyl, alkylaryl and diaiyl sulfides, via a proposed ClFe(TPP)0 intermediate the axial ligand trans to the 0x0 ligand is likely critical. The chemistry of eq. 27 would imply that Ru(porp)(0)(OSR2) is a more efficient 0-atom donor than Ru(porpXO)2, while data for phosphine oxidation (see Section 3.1) imply that the Ru-monooxo species disproportionates more quickly than reacting with phosphine. The kinetic data for thioether systems could be consistent with the type of mechanism described for the phosphine systems, and a careful re-evaluation of the thioether systems is needed. With Fe systems, of course, disproportionation to a dioxo species is unknown. Relevant to this discussion are the findings that LRu(porp)(0) species are better catalyst precursors than the corresponding Ru(porp)(0)2 for oxidation of saturated hydrocarbons... 

The Pd-catalyzed intramolecular oxidative C-H/C-H coupling of diaryl sulfides to form DBTs was developed by Zhou and coworkers (Scheme 4.5) [9]. This approach afforded various DBTs in moderate to good yields with tolerance of a broad range of substrates. Remarkably, the benzo[l,2-fi 4, 5-fi ]bis[fi]benzothiophene was successfully synthesized by this protocol, which could be used as an organic semiconductor for field-effect transistors. Furthermore, they found that diaryl sulfides bearing electron-rich substituents... 

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