Selenophene 1,1-dioxides

Selenophene 1,1-dioxides have been found to be more thermally labile than the corresponding thiophene 1,1-dioxides. While dimerization is often observed in the thermal decomposition of the latter, the neat thermolysis of selenophene 1,1-dioxides leads primarily to ring-opened products. For example, thermolysis of 2,3,4,5-tetraphenyl-selenophene 1,1-dioxide 5 gave a variety of a ring-opened products (Equation 1) <1998H(48)61>, whereas thermolysis of compound 5 in toluene leads to the formation of 2,3,4,5-tetraphenylfuran. 

There were no reports of the reactivity of substituents attached to the selenium atom of selenophenes. The oxidation of selenophenes to selenophene-Toxides and selenophene-1,1-dioxides is discussed in Section 3.13.5.2. 

Although the chemistry of selenophene 1,1-dioxides seems equally fruitful, it has been much less studied. It is only recently that the first successful synthesis of selenophene 1,1-dioxides appeared [254,255]. Oxidation of tetraarylseleno-phenes 198 with m-CPBA did not afford the corresponding selenophene 1,1-dioxides. The reaction produced E- 1,2-diaryl- 1,2-diaroylethylenes 199 as the prin-... 

The chemistry of selenophene 1,1-dioxides is thus only now beginning to be investigated. Much yet remains to be discovered, in the development of a fruitful field of heterocyclic and heteroatom chemistry. 

Little has been reported on the oxidation of selenium functionalities by dioxiranes. One case is the oxidation of selenophenes by DMD " at subambient temperatures. Good yields of either the selenophene 1-oxide or 1,1-dioxide may be achieved, which depends on the amount of DMD used (Scheme 12) . These results are similar to those already presented for the sulfur congeners. ... 

The absence of any derivatives of selenophene or tellurophene from the chemical catalogues makes their laboratory synthesis an unavoidable point of departure for any study of their chemistry or other properties. As the range of potential organic selenium or tellurium precursors is also extremely restricted, there has been particular emphasis on routes starting from simple inorganic species such as the elements themselves, the dioxides, the halides, the dihydrides and, in the case of selenium, the selenocyanate anion. 

The principal electrophiles to attack ring selenium are either oxidants or alkylating agents. Oxidation of substituted selenophenes and 2-benzoselenophene with an excess of 2,2-dimethyldioxirane leads to 1,1-dioxides, whereas oxidation of... 

The most common methods for the preparation of 1-benzoselenophene and its analogs involve the annulation of the selenophene ring onto a benzene substrate. Early works, such as reaction of selenium with phenylacetylene or the reaction of selenium dioxide with styrene, gave low yields but more recently elaborated procedures, e.g., gas-phase reaction of cinnamaldehyde with dimethyl diselenide at 630 °C, give 1-benzoselenophene in high yield [131, 132],... 

Yur ev and Khmel nitskii39 developed a synthesis of selenophene and its homologs from the reaction of paraffins, olefins, or conjugated dienes with selenium dioxide in the presence of chromic oxide on alumina at 450°-500°C. 

No diacylated selenophene can be obtained by direct acylation however, 2,5-diacyl-3,4-dihydroxyselenophenes (3) were obtained from 1,3,4,6-tetraketones and selenium dioxide in dioxane.69... 

Methyl selenien-2-yl glyoxal,118 the simplest a-diketone of the selenophene series, has been obtained in two ways by oxidation of 2-propionylselenophene by selenium dioxide and by hydrolysis of the product resulting from nitrosation of that ketone. Its UV spectrum has three characteristic maxima (Amax 277, 283, and 310 mp). When... 

Additional examples of selenophene ring-formation reaction that result from the treatment of 1,4-dienes with selenium dioxide have been reported. For example, treatment of verbenone derivative 116 with selenium dioxide in the presence of pyridine gave fused selenophene 117 in 92% yield (Equation 19) <20010L3161, 2002JOC6553>. Additional applications of this reaction include taxol analog 150 <1997BML1941> and a [l]benzopyrano[3,2-/ ]-selenophene-9-one derivative <2001SAA1427>. 

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