Selenones to selenoxides

The oxidation of selenoxides to selenones is slow requiring drastic conditions to be used. Diaryl, aryl methyl and dimethyl selenones are prepared by the oxidation of the ctxresponding selenoxides with prolonged exposure to KMn04 or ozone. The direct oxidation of selenides to selenones by FWO with ruthenium(II) complex catalyst, and C u(Mn04)2 has also been described. Aiyl trifluo-... 

Selenides (R2Se) can be oxidized to selenoxides and selenones. It is possible to oxidize a thioether to a sulfoxide in the presence of an alcohol moiety using MnOa/HCl. ... 

Selenones.1 Oxidation of selenides to selenones is hampered by the ready decomposition of the intermediate selenoxides. The most useful oxidants are per-acids (m-ClC6H4C03H, CF3C03H) and KMn04 (CH2C12-H20, 20°). 

Selenides are also nucleophilic and produce isolable selenonium salts (9) when treated with alkyl halides. They are easily oxidized to selenoxides (10) and further to selenones (11) under more forcing conditions (see Section 4). Reduction of selenides to the corresponding hydrocarbons is most conveniently achieved with nickel boride,or with tri-n-butyl- or triphenyltin hydride under radical conditions. " Other reagents for reductive deselenization include Raney nickel, lithium triethylborohydride, and lithium in ethylamine (Scheme 4). Benzylic selenides undergo radical extrusion reactions under thermal or photolytic conditions to produce... 

As a consequence of the selenoxide instability, the oxidation into selenones is only possible if the syn-elimination reaction becomes difficult, as in the case of strained structures. Under these conditions, the selenone is deprotonated and the a-selenonylalkyllithiums formed can react as other selenium-stabilized car-banions. It must be added that the seleninyl [PhSe(O)-] and selenonyl [PhSe(02)-j substituents behave as very good leaving groups. Vinylic selenoxides and selenones can undergo an intramolecular displacement of the selenium moiety after nucleophilic addition to the double bond under basic conditions. Cyclopropanes and oxetanes have been synthesized in this way [1,2]. 

Like sulfides, selenides can be oxidized to the corresponding oxides, selenoxides, or to selenones. Oxidation to selenoxides is much faster and, with some oxidants, final. Reaction conditions are specified in equation 592 for the oxidation of methyl phenyl selenide [325, 711, 773, 1034]. 

Lithium enolates derived from methyl ketones and acetates successfully add to vinyl selenoxides - and to vinyl selenones to give cyclopropyl ketones and esters (Scheme 110). The a-lithioalkyl selenoxide or selenone intermediates presumably exchange to the lithium enolates which, after displacement of the seleno or selenoxy group, lead to the observed products. 

Vinylic ether-containing Claisen rearrangement substrates may be generated using syn-elimination reactions of sulfoxides, selenoxides, and selenones. 2-(Arylsulfinyl)ethyl ethers are particularly useful substrates in these reactions because of their ready availability by nucleophilic addition of allylic alcohols to commercially available phenylsulfinylethene. Scheme 13.27 shows a typical synthetic context for this chemistry, involving the stereospecific introduction of quaternary centers from easily accessed allylic alcohol precursors." ... 

Conductometric studies demonstrated that alkyl selenoxides and selenones are completely ionized bases in chlorosulfonic acid, whereas the corresponding phenyl compounds and their nitro derivatives are only weakly basic. The selenones were found to be stronger bases than the corresponding sulfones. ... 

The chemistry of selenones (11) has not been studied as extensively as that of selenoxides. However, it has been demonstrated that selenones function as good leaving groups, comparable to tosylates or hahdes. For example, they are readily solvolyzed in methanol and produce rearranged products when -substituents with high migratory aptitudes are present (equations 7 and 8). Vinyhc selenones also act as Michael acceptors, as in the first step of the process shown in equation (9). 

The structures of organic selenium compounds are closely related to those of the homologous sulfur compounds. However, in sharp contrast to organosulfur compounds, most of the organoselenium derivatives contain the divalent, dicoordinate selenium atom. Tetravalent, tricoordinate selenium compounds such as selenoxides, selenonium salts and seleninic acids are much less common. Only a few hcxavalent selenium compounds such as selenonic acids and selenones are known. Thus, asymmetric C —Se bond formation is limited to creation of a carbon — selenenyl bond. 

Synthesis of a-Selenoalkyl Metals by Addition of Organometallics to Vinyl Selenides, Vinyl Selenoxides and Vinyl Selenones... 

Among these methods, the metallation reaction is the method of choice for selenides bearing electron-withdrawing groups able to stabilize the carbanionic center. This also applies to selenoxides, selenones and selenonium salts. 

Additions of various nucleophiles to vinyl selenoxides - and vinyl selenones have been described. Thus potassium hydroxide and amines add to vinyl selenones and directly produce epoxides and aziridines, respectively, whereas 3-methoxyoxetanes have been obtained from 7-hydroxy-a-alkenyl selenones and st ium methoxide (Scheme 111). ... 

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