Selenium-containing compounds, syntheses

Benzoselenophene [111, 112] and related fused selenophenes [113-116] were previously obtained via tedious multistep reactions involving a selenocyclization reaction from barely accessible selenium-containing compounds. Such conventional synthetic methods are unsuitable for the development of selenophene-based OFET materials. Sashida s group developed a simple one-pot preparation of benzoselenophenes by an intramolecular selenocyclization reaction of acetylene compounds with a selenolate anion [117, 118]. This allowed straightforward access to sophisticated fused selenophenes, such as 52 and 53, from commercially available chemicals [119, 120]. Scheme 6.9 depicts the key selenocyclization reaction used in the synthesis of 52. This synthetic protocol was also successfully applied to the synthesis of regioisomer 54 [121]. 

The formation of the selenium-containing product 141 during the reaction of selenium dioxide with hydroxydio-lefins 140 has been confirmed through the synthesis and reactivity studies with selected model compounds (Scheme 14). The isolation of 8-oxa-3-selenabicyclo[3,2,l]octanes and dimeric selenium compounds has been observed with cyclohexanyl and cyclopentanyl derivatives <1993JOC7942, 1995TL8097>. 

Compound 142 is a useful synthon for the synthesis of other selenium-containing heterocycles (48, 49). 

Polymer-supported reagents have attracted growing interest because they can be applied to combinatorial chemistry and solid-phase synthesis. Some newly developed selenium-containing polymers have been reported recently. These polymers show selective reactivity without forming toxic and odorous byproducts in the form of low-molecular-weight selenium compounds. 

This volume has been divided (arbitrarily) into seven chapters. Chapter 1 contains some interesting syntheses of sulfur- and selenium-containing coordination compounds and clusters including the synthesis of the [Fe4S4(SR)4]2 species which R. H. Holm so elegantly identified as models for active sites in nonheme iron proteins. Compounds formed from S22 and S52 are described. A convenient synthesis of CSe2 is reported. Several additional compounds relevant to biological sulfur chemistry are described. 

Inorganic selenium compounds are metabolized by reduction to selenide, followed by methylation or enzymatic conversion to selenophosphate, which serves as the reactive form of selenium for the synthesis of selenocysteine-containing selenoproteins. Whereas selenite requires no specific activa-... 

In spite of the large number of literature citations included in this Chapter, many of the routine papers on preparative chemistry have been excluded. The fact that so much work has been considered worthy of inclusion in this review on the basis of novelty and importance testifies as much to the intricacies and surprises still being found in the chemistry of sulphur- and selenium-containing functional groups as to the continuing growth in importance of these compounds in organic synthesis. 

Common synthesis of disulfonium dications involves formation of a S-S bond by oxidative coupling of two sulfide moieties. Involving for oxidative generation of S-S bond, thiocarbonyl compounds can lead to new-type dications containing disulfide moieties between two positively charged fragments. There are several disulfide dications of this type derived from thioureas, thiocarbon-ates and thioketones as well as selenium derivatives.137 148... 

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