Thiiranium ions isomerization

The nonstereospecific products are formed in both the reaction of stable thiiranium ions with nucleophiles and the addition of arenesulfenyl chlorides to alkenes. The reaction of the isomeric stable ions (158) and (159) with acetic acid at room temperature gives the same mixture of erythro-(160) and threo-( 161) products (Scheme 59) <75TL245i, 76IZV1318). Nonstereospecific products are also formed by the addition of 2,4-dinitrobenzenesulfenyl chloride to ( )- and (Z)-anisole <72JOC3086> and 4-methoxy-/ -deutereostyrene <84TL4983>. 

Thiiran reacts with chlorine and hydrochloric acid to give 2-chIoroethane-sulphonyl chloride in 85% yield. Derivatives of a-methylthioglycidic acid are cleaved readily by methane- or arene-sulphenyl chlorides to mixtures of isomeric disulphides, aCHaCMe(SSR)COX and KSSCH CMeCCOCOX (X = OMe, NH2, NMej, or NHPh R = alkyl or aryl), formed presumably via thiiranium ion intermediates. ... 

Electrophilic attack on the sulfur atom of thiiranes by alkyl halides does not give thiiranium salts but rather products derived from attack of the halide ion on the intermediate cyclic salt (B-81MI50602). Treatment of a s-2,3-dimethylthiirane with methyl iodide yields cis-2-butene by two possible mechanisms (Scheme 31). A stereoselective isomerization of alkenes is accomplished by conversion to a thiirane of opposite stereochemistry followed by desulfurization by methyl iodide (75TL2709). Treatment of thiiranes with alkyl chlorides and bromides gives 2-chloro- or 2-bromo-ethyl sulfides (Scheme 32). Intramolecular alkylation of the sulfur atom of a thiirane may occur if the geometry is favorable the intermediate sulfonium ions are unstable to nucleophilic attack and rearrangement may occur (Scheme 33). 

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