Aryl sulphoxides

Partial photochemical decomposition of racemic alkyl aryl sulphoxides in the presence of chiral amines as sensitizers gave non-decomposed sulphoxides in optically active form with optical purity of about 3%339. The report340 on the use of cholesteric liquid crystalline reaction media to change the enantiomeric composition of racemic sulphoxides at high temperatures could not be reproduced341. 

As mentioned above, 1-alkenyl aryl sulphoxides can effectively be a-lithiated by treatment with a slight excess of LDA in THF at — 78°. The 1-(arylsulphinyl)alkenyllithium reagents 331 so generated react cleanly and rapidly with a variety of electrophiles to give 1-substituted 1-alkenyl sulphoxides 332 in high yields (equation 191). 

Addition of the anions of allyl aryl sulphoxides 407 to benzaldehyde proceeds readily and affords a mixture of products resulting from both a- and y-attack of the allyl anion483 (equation 240). In the case of the a-attack a mixture of all four possible diastereoisomers is observed, while in the case of the y-attack, the diastereoisomer ratio exceeds 2 1. 

In the case of a-chloroalkyl aryl sulphoxides, the chloroalkyl group is easily replaced by an alkyl or aryl group of a Grignard reagent (equation 370). Bromomethyl sulphoxides react slowly and give the products in low yields, while iodomethyl sulphoxides are unreactive presumably due to steric hindrance (Table 29)678. 

Another marked physical difference between sulphides and sulphoxides (or sulphones) is that sulphoxides (and lower alkyl sulphones) are hygroscopic and dissolve quite readily in water or protic solvents such as alcohols, and even more so lower alkyl or alkyl aryl sulphoxides are almost freely miscible with water. This can be accounted for by the formation of the strong hydrogen bond between the S—O bond in the sulphoxides and water molecules. Moreover, lower alkyl sulphoxides and sulphones such as dimethyl sulphoxide (DMSO) or sulpholene can dissolve a number of metallic salts, especially those of alkali and alkaline earth metals, and hence these compounds have been widely utilized as versatile and convenient solvents in modern organic chemistry26 (Table 3). 

Oxidation of either alkyl or aryl sulphoxides to sulphones in 65-90% yields may be accomplished by treatment with a nitronium salt15. In the case of aryl sulphoxides no nitration is observed (which is in contrast to the results of nitric acid oxidation). The reaction was shown to proceed through intermediate nitratosulphonium and nitritosulph-oxonium ions, as depicted in equation (7), which were studied by nmr spectroscopy. 

It is rather surprising that more studies in this area have not been reported, especially since the yield in the case of diphenyl sulphoxide oxidation is good and the product is easily separable from other materials formed in the electrochemical cell. Presumably more reports will be forthcoming in the next few years, especially for the oxidation of aryl sulphoxides. 

Sulphonylthioureas, mass spectra of 158 Sulphoxides - see also Alkoxysulphoxides, Aminosulphoxides, -Anilinosulphoxides, Cyanosulphoxides, a, /i-Dihalosulphoxides, Disulphoxides, Enaminosulphoxides, Episulphoxides, Epoxysulphoxides, Halosulphoxides, Hydroxysulphoxides, /i-Iminosulphoxides, Ketosulphoxides, a-Lithiosulphoxides, /i-Oximinosulphoxides, Persulphoxides, a-Thioamidosulphoxides addition reaction of 619-623, 836-845 aliphatic - see Aliphatic sulphoxides alkenyl - see Alkenyl sulphoxides alkyl aryl - see Alkyl aryl sulphoxides /(-alkylthio(arylthio)ethyl - see /J-Alkylthio(arylthio)ethyl sulphoxides... 

The reaction of alkyllithium reagents with diaryl or alkyl aryl sulphoxides results in a displacement of the aromatic group by the alkyl group from the alkyllithium (equation 369) . Johnson and coworkers ° were the first to apply this reaction for the synthesis of optically active alkyl methyl sulphoxides. Later on. Durst and coworkers found that the aromatic group which can best carry a negative charge is the most readily displaced, and that the lowest yields of displacement were observed when methyllithium was used as a nucleophilic reagent. The results are summarized in Table 28. 

This reaction was discovered while studying the mechanism of racemisation of optically active of aryl sulphoxides. 

More recent developments in the field of the Pirkle-type CSPs are the mixed r-donor/ r-acceptor phases such as the Whelk-Of and the Whelk-02 phases.The Whelk-Of is useful for the separation of underiva-tized enantiomers from a number of families, including amides, epoxides, esters, ureas, carbamates, ethers, aziridines, phosphonates, aldehydes, ketones, carboxylic acids, alcohols and non-steroidal anti-inflammatory drugs.It has been used for the separation of warfarin, aryl-amides,aryl-epoxides and aryl-sulphoxides. The phase has broader applicability than the original Pirkle phases. The broad versatility observed on this phase compares with the polysaccharide-derived CSPs... 

DNBLeu (covalent).5 Chiral phases S-Asp-artyl-S-phenylalanine methyl ester, N.N- Di-propyl-S-alanine cupric acetate. Phosphonates, aryl-sulphoxides, nitrogen heterocycles, di-B-naphthols. 

Earlier, attention was drawn to a novel application of the oxidative desulphurization reaction which occurs between sulphoxides and phosphonothioic acid esters. When 1 mol of the thio acid is allowed to remain in contact with 2 mol of a racemic methyl alkyl sulphoxide for 2 weeks at room temperature, the unreacted sulphoxide is found to be optically active, a result which represents asymmetric deoxygenation of the sulphoxide. The chemical course of the reaction is consistent with Scheme 31. Since the appearance of the initial results, corrections have been made to the configurations of the phosphorus-containing substrates, and hence the stereochemical details and mechanistic arguments require reappraisal neverthless, the fact remains that (-t-)-sulphoxides are obtained by the use of the ( S)-(-)-acids, R (R O)P(S)OH , a feature which can be used to determine the chirality of other like acids. Dialkyl and alkyl aryl sulphoxides are also known to form diastereoisomeric complexes with (5)-(-)-/er butylphenylphosphinothioic acid, distinguishable by their NMR spectra, and through such complexation it is possible to assess the enantiomeric composition of the sulphoxide " ... 

Recently, Poli et al. have reported on the palladium-catalysed synthesis of arylic sulphoxides. These authors showed that sulphenate anions generated in situ from jS-sulphinyl esters can provide several aryl sulphoxides under biphasic conditions (06OL5951) (Scheme 18). The sulphoxides are obtained in good yields from the corresponding aryl iodides. However, the use of aryl bromides was unsuccessful. 

Pyrolysis of aryl sulphoxides gives rise to alkenes. Coupled with Michael addition of nucleophiles to aryl vinyl sulphoxides, a rather general synthesis of substituted alkenes results. Annulenophanes have been prepared by photolytic triethyl phosphite-induced desulphurization of cyclic bis-dialkylsulphides. ... 

Bu3SnCH2(Me3Si)C=CH2 couples with o-substituted aryl sulphoxides with syn stereoselectivity and allylates radicals while Mc3Si(R3Sn)CHCHsCHR result fiom the Pd catalysed reduction of the allyl acetate... 

Aryl sulphoxides 1060-1040 9.43-9.62 s m-w See refs 18, 19 CHCI3 solution spectra quite different... 

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