Sulfenyl halides reactions with alkenes

MO calculations for the gas phase indicate that sulfurane intermediate (17) is more stable than the ion (18) by about 380 kJ moP, which suggests that sulfuranes may be important in the reaction of sulfenyl halides with alkenes in non-polar solvents (77JCS(P2)1019). 

In agreement with the mechanism reported in equation 90, the reaction generally follows a second-order rate law (equation 92), first order in the sulfenyl halide and in the alkene, respectively. 

Mechanistic studies have been most thorough with the sulfenyl halides.63 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.64 The variation in regioselectivity can be understood by... 

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. 

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... 

Enolates react with sulfenyl halides to give an a-alkylthio ketone. As shown for cyclohexanone, reaction with LDA followed benzenesulfenyl chloride (PhSCl) produced phenylthio derivative 109. The proton adjacent to both the carbonyl and the sulfur (the a-proton) was more acidic and it was deprotonated with potassium hydride, forming the enolate, and alkylation with iodobutane gave a 91% yield of 110. As mentioned in Chapter 2, the sulfide moiety can be oxidized to a sulfoxide and thermally eliminated (syn elimination, sec. 2.9.C.v) to give an alkene. 9 Similar methodology can be applied to selenides, R—Se—R. O... 

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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