Preparation from Disulphides, Diselenides, and Ditellurides

Preparation from Disulphides, Diselenides, and Ditellurides.—The use of disulphides as sulphenylating agents towards alkenes and carbanions continue to offer a distinctive alternative to the use of sulphenyl halides for the same purpose. Although reaction conditions are more severe, cleaner results are usually obtained. The special case of the conversion of disulphides into corresponding sulphides is covered in the later section on Reactions of Disulphides. 

Irradiation of a mixture of MeSSMe and F2C=CH2 with u.v. light gives MeSCFjCHjSMe, a compound which can be prepared less conveniently from F2C=CHBr with MeSH and MeSNa. Anodic oxidation of disulphides in the presence of alkenes in MeCN gives yS-acetamidoalkyl sulphides  

Related double-functionalization procedures for alkenes have been established for the preparation of 2-acetoxyalkyl phenyl selenides [PhSeSePh with Cu(OAc)2 and AcOH], ° yff-hydroxyalkyl aryl sulphides [ArSSAr with Pb(OAc)4 and TFA, for Markownikov trans-hydroxysulphenylation ], and )ff-ketoalkyl selenides [PhSeSePh with Br2 and (Bu 3Sn)20].  

2-Arylsulphenylation of 1,3-dicarbonyl compounds cm be effected at room temperature in an Et4N+ F emulsion, but dianions R CHCOCHCOR, formed by successive treatment with NaH and Bu Li, are sulphenylated at the alternative site by RbSSPh. 8-Keto-esters, malonates, and a-cyanoalkanoates can be sulphenylated and decarbalkoxylated in a one-pot process by reaction at 150—160 C, in HMPA, with PhSSPh and Nal, providing a-(phenylthio)alkyl ketones, cp(phenylthio)alkanoates, and tf-cyanoalkyl phenyl sulphides. 

A singlet benzyne intermediate is involved in the conversion of diaryliodonium 2-carboxylates into o-diselenides, o-ditellurides, and o-arylselenoaryl aryl tellurides by reaction with ArSeSeAr, ArTeTeAr, or ArSeTeAr respectively.  

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