Sulfenyl halides, addition reactions

Mechanistic studies have been most thorough with the sulfenyl halides. The reactions show moderate sensitivity to alkene structure, with electron-releasing groups on the alkene accelerating the reaction. The addition can occur in either the Markownikoff or anti-Markownikoff sense. " The variation in regioselectivity can be understood by... 

Simple 1,2-additions to this compound have been observed123131132 also in other sulfenylation reactions, and in other electrophilic additions involving strongly bridged intermediates. Although these results have been interpreted as evidence that additions of sulfenyl halides to symmetrical alkenes do not involve open carbenium ions before the product-determining step, the different behavior observed in the case of 49 suggests123 that close proximity is necessary to have transannular participation of 7r-bonds, at least in additions of sulfenyl derivatives and of some other electrophiles carried out in the presence of efficient nucleophiles. 

Addition of a selenenyl halide to an alkyne takes a course analogous to that of the sulfenyl halide, as seen in the reaction of l,4-dichlorobut-2-yne with PhSeCl or PhSeBr (Scheme 19).28-62 Selenenyl halides also undergo facile addition to allenes with exclusive attack by selenium occurring at the central allenic carbon.63... 

Addition of sulfur chlorides and sulfenyl halides to hydrocarbon olefins is a classic example of electrophilic reaction which usually proceeds under mild conditions and results in stereospecific trans-addition via intermediate formation of cyclic episulfonium cation [134]. Ring-opening reactions of episul-fonium cation with nucleophile is responsible for formation of regioisomers when nonsymmetrical olefins are used as substrates. 

Shortly after World War II, a research chemist at the Standard Oil Development Company (Esso) strolled into an oil additive laboratory and saw an interesting intermediate called perchloro-methyl mercaptan (CCI3SCI). A. F. Kittleson, spurred by visions of the trichloromethyl group in that then new miracle drug DDT, decided to try some reactions with the above described sulfenyl halide. 

The addition of sulfenyl halides across a double bond is a well-known reaction and is mainly used for the synthesis of //-halo sulfides. The first report on the steric course of this reaction concerned the addition of 2,4-dinitrobenzenesulfenyl chloride to ( )- and (Z)-2-phenyl-2-butene15. The addition to each isomer produces different crystalline derivatives as racemic pairs. 

Further studies on the reaction of sulfenyl halides with alkenes established that the addition occurs in an anti fashion. In this manner, syn- and nh-/j-chloroalkyl aryl sulfides were prepared by addition of arylsulfenyl chlorides to (Z)- and ( )-butene16. 

J-Alkyl- or -arylthio amines were obtained by nucleophilic attack of an amine on episulfonium ions generated by reaction of sulfenyl halides or tetrafluoroborates with alkenes15-18. An effective azasulfenylation was also induced by dimethyl(methylthio)sulfonium tetrafluorobo-rate (DMTSF) in the presence of amines. With this latter reagent ammonia also adds to a double bond19. ant/ -Addition products are exclusively formed. 

Sulfenyl halides (1) will also undergo nucleophilic addition with alkenes (Scheme 1) to yield the episulfides (7), which can suffer a further nucleophilic addition to give the sulfides (8). The nucleophilic substitutions of sulfenyl (1) (see Chapter 4, p. 54) and sulfonyl (3) chlorides (see Chapter 7, p. 106) probably generally proceed by the SN2 reaction mechanism, which with the sulfonyl halide (3) involves the trigonal bipyramidal transition... 

Addition of the fluorinated sulfenyl halides to olefinic bonds occurs readily for example, with ethylene and 24 the reaction gives 25. Similar reactions occur with unsaturated polymers to generate crosslinks. 

The reactions of carbonimidoyl dihalides can be divided into nucleophilic substitution reactions, whereby the halo groups are replaced stepwise by other nucleophiles, and addition reactions. The substitution reactions are often accompanied by elimination, depending upon the stability of the formed imidoyl derivatives. For example, the monosubstitution products can eliminate hydrogen halide, alkyl halide, or sulfenyl chloride, i.e.,... 

This reaction has been modified to use a sulfoxide as a synthetic equivalent of a sulfenyl halide. In addition, a procedure that involves the initial mixing of ethyl (methylthio)acetate and sulfuryl chloride, followed by the addition of aniline with one equivalent of proton sponge and final EtsN treatment can be used to prepare oxindole that is not accessible via the initial Gassman protocol. ... 

Comparison of the structure-reactivity relationships for a series of styrene and alkene addition reactions with bromine and with arylsulfenyl halides also supports the idea that a bromonium ion is formed in the rate-determining step. From other evidence the sulfenyl halides are known to add through a bridged intermediate and the similarity between the two reaction series points to a closely similar transition state. 

The less polar nature of disulfides and sulfenamides makes the addition of these reagents to alkenes inefficient. Although thiolates can be generated under reducing conditions,the activation of disulfides and sulfenamides is routinely performed by Lewis acids to enable the introduction of new u bonds other than C—S bonds. As a consequence, the stereospecificity and reactivity observed in the Lewis-acid-promoted addition of disulfides and sulfenamides to alkenes is similar to that of sulfenylation by sulfenyl halides and thi-osulfonium salts. Likewise, the accepted reaction mechanism includes the coordination of Lewis acid, resulting in a thio-sulfonium-like species that can further react with alkene either directly or indirectly by way of dithiosuhonium ions. 

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