Alkenes sulfenyl halides

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). 

The addition of sulfenyl halides to both alkenes and alkynes had been the subject of extensive mechanistic study. The salient results up to about 1969 have been reviewed by Mueller (1969) and Modena and Scorrano (1968). Considerable additional work on various aspects of the detailed mechanisms has been done since that time by Schmid and his co-workers (Schmid and Csizmadia, 1972 Schmid et al., 1972 Schmid and Nowlan, 1976 Schmid et al., 1976b Cerksus et al., 1978). A recent short review by Smit et al. (1979) criticizes some aspects of earlier interpretations of mechanism. 

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. 

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. 

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... 

Several types of sulfenyl chlorides are known. Sulfur monochloride and dichloride can add to dienes forming sulfor bridges. - The most commonly used sulfenyl halides are benzenesulfenyl dilorides and methanesulfenyl chloride. Other sulfenyl halides, such as acetylthiosulfenyl chloride and thiocyanogen chloride, have been added to alkenes, but few subsequent transformations have been carried out with those intermediates. 8... 

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. 

The stereoselective tram addition of sulfenyl halides and other sulfenyl derivatives to alkenes can be rationalized by assuming a bridged thiiranium ion, by analogy with the mechanism proposed for stereoselective halogenation of alkenes. 

In contrast to sulfenyl halides, which react readily with alkenes at room temperature, sulfenic esters show much lower electrophilic reactivity towards alkenes. Methyl 2-nitro- and 2,4-dini-trobenzenesulfenates, however, add to cyclohexene on prolonged heating in methanol to form the Ow7.y-adduct 1 in moderate yield28. 

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... 

Alkenes 4.24, with a n orbital as the HOMO and no charge, are inherently soft nucleophiles, and their nucleophilicity ought to have some relationship to the energy of their HOMOs. The relative rates of attack by different alkenes have been measured for such electrophiles as bromine, peracids, sulfenyl halides, electrophilic 1,3-dipoles (Chapter 6), metal cations (Hg2+, Ag+) and boranes. These electrophiles fall into two groups those like bromine, peracid and sulfenyl halides that show a correlation between the rate and the ionisation potential of the alkene, and those like 1,3-dipoles, metal cations and boranes, that show significant discrepancies.263 The first group show little sign of steric effects, since the more substituted alkenes, with the... 

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... 

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