Sulphoxides alkyl aryl

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. 

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). 

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. 

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 " ... 

In contrast to the asymmetric procedures discussed above, the metal-catalyzed oxidation of alkyl aryl sulphides by t-butylhydroperoxide carried out in a chiral alcohol gives rise to chiral sulphoxides of low optical purity290 (e.e. 0.6 9.8%). Similarly, a very low asymmetric induction was noted when prochiral sulphides were oxidized by sodium metaperiodate in chiral alcohols as solvents291. 

Much higher asymmetric induction was observed in the two-phase oxidation of simple alkyl aryl and diaryl sulphides296, substituted alkyl aryl sulphides297 and dithioacetals of formaldehyde298 by sodium metaperiodate in the presence of proteins such as bovine serum y-globulin and egg albumin. Optical purities of the sulphoxides so formed ranged between 20 and 85%. 

The Andersen sulphoxide synthesis is general in scope and a large number of chiral alkyl aryl and diaryl sulphoxides became available from (—)-(S)-276 and other optically active sulphinates343-346 (Table 16). 

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. 

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. 

Water insoluble tetrabutylammonium metaperiodate, which can be prepared from sodium metaperiodate and tetrabutylammonium hydrogen sulphate in aqueous solution, was found to be a useful reagent for the selective oxidation of sulphides in organic solvents . The reaction was generally carried out in boiling chloroform and gave dialkyl, alkyl aryl and diaryl sulphoxides in yields which are comparable with those reported for sodium metaperiodate in aqueous methanol solution (Table 4). In the case of diaryl sulphoxides, the yields decrease with prolonged reaction time. 

Stereoselective oxygen transfer to the sulphur atom of alkyl aryl sulphides catalyzed by 2-flavoenzyme monooxygenases afforded optically active sulphoxides in high optical yields . For instance, with ethyl p-tolyl sulphide as substrate cyclohexanone monooxygenase from Actinetobacter produces predominantly (— )-(S)-sulphoxide with 64% e.e. In contrast, FAD-containing dimethylaniline monooxygenase purified from hog liver microsomes affords (+ )-(i )-enantiomer of this sulphoxide with 90% optical purity . ... 

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