Organoselenium halides

Several inorganic compounds of selenium are known to contain secondary bonds, but only organoselenium derivatives will be covered here. Among these, the organoselenium halides are of interest, because selenium iodides were - for many years -considered not to exist the compounds have recently become available [477]. 

Table 2 Reduction of wganotellurium and organoselenium halides and ox-ides by TUD...

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. 

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. 

Reduction of Organoselenium and -tellurium Halides and Oxides. TUD reduces aryltellurium trihalides to diaryl ditel-lurides (eq 2) and diorganyltellurium dihalides and telluroxides to diorganyl tellurides (eq 3) in high yield. The corresponding selenium compounds are reduced similarly. Some examples are given in Table 2. The reduction is performed by premixing the substrate and 2 N NaOH at room temperature for 15 min prior to the addition of TUD in petroleum ether. 

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... 

Classically, treatment of an endocyclic enol ether with an electrophilic halide reagent such as iV-bromo- or A[-iodosuccinimide [72,113-117], or organoselenium reagents (PhSeX) [118-122], affords electrophUe-substituted spiroacetals (Scheme 53). The halide is then removed using reductive methods or used for further elaboration of the spiroacetal toward the target molecule. 

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