Selenium chemistry

Tellurium chemistry is often significantly different in comparison with selenium chemistry owing to the larger size and metallic character of tellurium (Section 1.1). As an illustration, the cyclocondensation of... 

Epoxldation of (12) with a nucleophilic agent occurred only from the outside of the molecule and the necessary oxidation to (7) could be carried out with RuC and NalO. The remaining steps required new reactions based on selenium chemistry and gave methylenomycin in 12% overall yield from maleic anhydride. 

Zingaro, R. A., and Cooper, W. C., Eds. (1974). Selenium. Van Nostrand Reinhold, New York. An extensive treatment of selenium chemistry. 

Selenium chemistry is complex, and additional research is warranted on chemical and biochemical transformations among valence states, allotropic forms, and isomers of selenium. 

This review is conceived as a progress report. It includes only compounds of selenium and tellurium with the element directly bonded to fluorine. The chemical literature of the last 10 years, including 1979, has been searched thoroughly, and emphasis has been placed on facts rather than on interpretation. There are some earlier reviews covering the same area "Fluorine Compounds of Selenium and Tellurium 1970 (40), "Inorganic Selenium Chemistry 1975 (48), and "Inorganic Chemistry of Tellurium 1975 (53). 

Linkers based on sulfur, stannane and selenium chemistry are certainly some of the most flexible systems, because these elements can favorably be tailored for the use as fragile points of attachment. 

Krief has applied selenium chemistry to some anionic cascade cyclisations.128 For example, 293 can be cyclised in two successive 5-exo reactions to give a mixture of the stereoisomers of 297. If 294 is warmed to 0 °C, an alternative sort of tandem process occurs after cyclisation onto the alkene, the organolithium 295 undergoes an intramolecular displacement, stereoselectively generating the 5,3-fused system of 296. Similar intramolecular cyclopropanations (of a-bromo organolithiums) have been described by Hoffmann151 but are probably mediated by carbenes rather than a sequential cyclisation-substitution sequence. 

This chapter concentrates on the developments in organoselenium chemistry from 1993 to 2004 and is therefore a continuation and extention of the chapter Selenium by Krief in the previous edition of Comprehensive Organometallic Chemistry,18 During that period many aspects of organoselenium chemistry have been covered in review articles19-35 and in books completely devoted to different areas of selenium.36-40 These reports highlight the current activities in selenium chemistry and stress the importance of selenium-containing molecules in different areas. 

Sulfur and selenium have many properties in common. and much sulfur chemistry is mirrored by selenium chemistry, in general, organoselenium compounds tend to be less stable and more reactive than organosulfur ones because the C-Se bond is even weaker than a C-S bond. They also have even fouler odours. 

It is possible to oxidize an alcohol in the presence of sulfur- or selenium-containing groups (equation 16) using r-butyl hydroperoxide and a diselenide as the oxidizing system (this also oxidizes secondary alcohols, see later).Selenium chemistry can also be used to oxidize benzylic and related primary alcohols to the aldehydes without oxidizing pyridyl (18 equation 17) or thiophenyl (19 equation 18) groups. ... 

Other areas of selenium chemistry, such as selenium rings, selenides, " organoselenium compounds, " and the focus of older, more comprehensive accounts of Se halide chemistry will not be covered here. Additionally, the vast environmental chemistry of selenium, for example, its aqueous and sediment speciation, plant uptake, nutritional and human health aspects, and appearance in coafl and coal-derived ash, are beyond the scope of this review. The previous reviews on Se-containing ligands, " biochemistry of selenium,as well as other relevant aspects, remain some of the most valuable sources for information on these subjects. 

In the following sections, typical methods for the preparation of nucleophihc selenium species are described, followed by their general utility in various nucleophihc reactions. Subsequently described are unique reactions using selenium reagents having a selenium to main-group element bond as an alternative source to nucleophihc selenium species. Two recent topics, i. e. applications to asymmetric and solid-phase syntheses, are presented separately. Finally, the perspectives of nucleophihc selenium chemistry are discussed. 

Earlier synthetic applications of selenium dioxide for the introduction of the carbonyl functionality at activated positions, to dehydrogenation of highly activated saturated sites, to hydroxylation of activated carbon-bearing positions, particularly at allylic(propargylic) sites, and to oxidative bond cleavage are presented in a few books devoted to selenium chemistry [2] or oxidation reactions [14]. These procedures are also permanently included in the Fieser Fieser compendium of reagents [15]. 

As an application of selenium chemistry, reduction of aryl ketones with CO and H2O in the presences of selenium and DBU has been carried out. The reduction, indicated in Scheme 19, can be considered as a redox reaction by CO and H2O. This reaction proceeds in high yield with only a catalytic amount of selenium. Although the reaction mechanism has not been clarified, this reaction probably involves an or-ganoselenium hydride intermediate (60), which is known to give the corresponding hydrocarbon under the reaction conditions." ... 

Finally, the double bond is introduced by selenium chemistry (p. 1271). The steps r-. straightforward and the geometry of the alkene is dictated by the ring. 

Krief A., Hevesi L. Applications of Selenium chemistry to Organic Synthesis, Springer-Verlag, Berlin, Heidelberg in the Press... 

Ethyl diethylphosphonoacrylates can be produced by either sulfur or selenium chemistry. These react with salicylaldehydes to give dihydro-benzopyrones. Condensation with 2-hydroxycyclohexanone gives the hexa-hydrobenzofuran. ... 

ParnhamMJ. 1996a. The pharmaceutical potential of selenium chemistry. 3(5) 7-10. 

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