Preparation of Organoselenium Compounds

Support-bound organoselenium compounds have mainly been used as synthetic intermediates and linkers. The use of organoselenium compounds as linkers for solid-phase synthesis has been investigated by several groups [1-4]. The selenium-carbon bond is stable under a broad variety of reaction conditions, but can be selectively cleaved by tin radicals or by oxidants (see Sections 3.15.1 and 3.16.4). 

The reaction of suitably functionalized alkenes with polystyrene-bound selenyl bromide can lead to cyclization of the alkene by C-C, C-O, or C-N bond formation with simultaneous attachment to the support. The cyclic product can then be released from 

---

A highly stereoselective preparation of organoselenium compounds having a chiral center at the selenium atom... 

However, the attractiveness of selenium in radical reactions is not only caused by the above mentioned radical properties of organoselenium compounds. The rich chemistry of selenium has also been an important factor since it allows a facile preparation of stable radical precursors as well as attractive functional group transformations when the selenium moiety remains in the reaction products. The different sections of this chapter have been arranged according to reaction types. 

Despite the toxicity of organoselenium compounds, they are routinely applied as precursors for radical reactions. This is due to the unrivaled quality of organoselenium compounds in term of stability, ease of preparation and ease of homolysis of the carbon-selenium bond. Their rich chemistry will continue to make them particularly attractive for the development of new radical processes. This is particularly true when complex systems are examined, such as radical precursors for cascade reactions. Moreover, processes where organoselenium derivatives are used in catalytic amounts will become more attractive and environmentally more friendly. 

These facts, together with many other examples of the peculiar chemical behavior of organotellurium compounds (95UK527), emphasize their specific reactivity and explain why a number of methods developed for preparation of organosulfur and organoselenium compounds are inapplicable for their tellurium analogues. 

Used industrially for preparation of metallic selenides, organoselenium compounds, and preparation of semiconductor materials. 

The organoselenium compounds, their chemistry, and methods of preparation are discussed in the literature (3,4,7,11,12,14,59). Selenium-containing polymers are of interest because of their semiconducting and plastic properties. The biologically important compounds include selenoaminocarboxylic acids and derivatives, selenium-containing peptides, and selenium derivatives of pyrimidines, purines, cholines, steroids, coenzyme A, and other compounds (4,14). The biochemical and medical aspects and uses of oiganoselenium compounds have also been discussed (13,14,60—62). 

Figure 9.1. Strategies for the preparation of polystyrene-bound organoselenium compounds [1,2],...

Also widely employed are organoselenium compounds containing group 14 elements. Phenyl trimethylsilyl selenide 102 can be easily prepared from diphenyl diselenide 8 and is a good source for selenium nucleophiles (Scheme 24). In the presence of methanol selenols are generated for use in Michael reactions or in ring-... 

Organoselenium compounds are very versatile radical precm-sors which are widely used. Due to their stability and ease of preparation, they offer imique advantages over organic halides as radical precm-sors. They can be utilized in tin mediated radical reactions as weU as in group transfer reactions for the formation of carbon-carbon bonds and carbon-heteroatom bonds. Selenols and diselenides have found applications as reducing agents and radical traps, respectively. A survey of these different reaction types wiU be given. Information about new reactions based on electron and photoelectron transfers wiU also be provided. 

Finally, ultrasound has been used in the preparation of a variety of organoselenium and organotellurium compounds by reaction of alkyl halides, tosylates, mesylates and epoxides with the phenylselenium anion [107] and... 

They also carried out preparative scale gas chromatograph (Wilkins Instrument and Research Inc. Model, Aerograph A-90-P) for the purification of synthesized organoselenium compounds. The column used for the preparative gas chromatography was 5ft x I in.,... 

---