Sulfenylation and Selenenylation

The stereochemistry of both chlorination and bromination of several cyclic and acyclic dienes has been determined. The results show that bromination is often stere-ospecifically anti for the 1,2-addition process, whereas syn addition is preferred for 1,4-addition. Comparable results for chlorination show much less stereospecificity.It appears that chlorination proceeds primarily through ion pair intermediates, whereas in bromination a stereospecific anfi-1,2-addition may compete with a process involving a carbocation intermediate. The latter can presumably give syn or anti product. 

Entry 4 is a special type of sulfenylation agent. The sulfoxide fragments after O-acylation, generating a sulfenyl electrophile. 

Entries 12 to 14 are examples of oxidative generation of selenenylation reagents from diphenyldiselenide. These reagents can be used to effect hydroxy- and methoxysele- 

Entry 15 shows A-(phenylselenyl)phthalimide, which is used frequently in synthetic 

Tiecco, L. Testaferri, A. Temperini, L. Bagnoli, F. Marini, and C. Santi, Synlett, 1767 (2001). 

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The synthesis ofvernolepin Halolactonisation in the synthesis of erythronolides Sulfenyl- and Selenenyl-Lactonisation The Prins Reaction... 

In this chapter, we discuss reactions that either add adjacent (vicinal) groups to a carbon-carbon double bond (addition) or remove two adjacent groups to form a new double bond (elimination). The discussion focuses on addition reactions that proceed by electrophilic polar (heterolytic) mechanisms. In subsequent chapters we discuss addition reactions that proceed by radical (homolytic), nucleophilic, and concerted mechanisms. The electrophiles discussed include protic acids, halogens, sulfenyl and selenenyl reagents, epoxidation reagents, and mercuric and related metal cations, as well as diborane and alkylboranes. We emphasize the relationship between the regio-and stereoselectivity of addition reactions and the reaction mechanism. 

The most noteworthy feature of the sulfenylation and selenenylation rates (represented by the triangles) is their much diminished sensitivity to substitution. This reflects both smaller electron demand in the TS and increased sensitivity to steric factors. The relatively low rate of styrene toward selenenylation is somewhat of an anomaly, and may reflect both ground state stabilization and steric factors in the TS. The epoxidation data (CH3CO3H, hexagons) show a trend similar to bromination, but with a reduced slope. There is no evidence of a rate-retarding steric component. One indicator of a strong steric component is decreased reactivity of the E-isomer in an E,Z—disubstituted alkene pair, but the rates for the 2-butene isomers toward epoxidation are very similar (Table 5.9). 

Third- and fourth-row substituents such as sulfenyl, sulfinyl, sulfonyl, phosphinyl, and selenenyl stabilize carbanions. Because these substituents have tetrahedral... 

Reviews cover transition-metal-catalysed enantioselective a-heterofunctionalization of carbonyl compounds (103 references)," and organocatalysed enantioselective a-hetero-functionalization from 2006 to 2009, demonstrating straightforward syntheses of useful a-amino acids and alcohols, epoxides, 1,2-diols, and a-sulfenylated, a-selenenylated, and a-halogenated carbonyl derivatives." ... 

Association of Sulfenyl, Selenenyl and Tellurenyl Halides with Chelating Substituents... 

The addition of phenyl sulfenyl choride and phenyl selenenyl chloride to glycals has been investigated, which provides another entry to the 2-deoxy-P-glucosides. As summarized by Roush et al. [156] (Scheme 5.53), the method gives the best selectiv-... 

This mechanistic picture is supported by the fact that the ketene acetal moiety in 170 can be trapped by suitable electrophiles providing adducts 171. Ring cleaving selenenylation and sulfenylation is therefore possible at —78 °C in the presence of a few drops of TiCl (Table 5, entries 1—5)91). Without Lewis acid no reaction with the sulfur electrophile could be observed at room temperature and incorporation of the phenylselenenyl group occurs only rather slowly. 

Heterofunctionalizations. Practically all the substrates are alkenylzirconocene chlorides. They behave well in halogenation, phosphorylation, sulfenylation, sulfiny-lation, selenenylation" and selenoacylation, as well as tellurylation," which gives rise to the substituted alkenes. 

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