Selenenates

Scheme 15.1 Catalytic cycle for the conversion of a diselenide to a selenenic acid...

In the second step of this reaction the O—O bond of H2O2 is cleaved. During this process, one hydroxyl fragment (0 11) is transferred to the selenolate anion (R—Se-) to form selenenic acid (R—SeO1 II), while simultaneously the second... 

Not only propargyl precursors but also acceptor-substituted 1-methyleneallyl compounds such as 67, 71 or 74 can be used to produce the target allenes by sigmatropic reactions (Scheme 7.10). After oxidation of selenium compounds 67 followed by equilibration of the resulting selenoxides 68 and selenenic esters 69, hydrolysis... 

M. T. Molina, M. Ydnez, O. M6, R. Notario and J.-L. M. Abboud the thial along with selenenic acid 67. 

Dehydrogenation of enones. Tl(OAc)3 can be as effective as DDQ or benzene-selenenic anhydride for dehydrogenation of a, 3-enones to 1,4-dienones. However, in some cases the reaction involves dehydrogenation, acetylation, and aromatization to catechols, as in the oxidation of 1 to 2. 

The use of allylic selenides 166 in oxidation reaction leads to intermediate selenoxides 167, which can undergo [2,3]sigmatropic rearrangements to the corresponding allylic selenenates 168. These componds will lead to allylic alcohols 169 after hydrolysis (Scheme 48). This is also a versatile procedure for the synthesis of optically active allylic alcohols, provided that either an asymmetric oxidation or an optically active selenide is used for the rearrangement. Detailed kinetic and thermodynamic studies of [2,3]sigmatropic rearrangements of allylic selenoxides have also been reported.290-294... 

Rheinboldt, H. In Schwefel, Selenen und Tellurverbindungen, Methoden der Organischen Chemie (Houben-Weyl) Muller, E., Ed. Georg Thieme... 

Selenides may be oxidized by various reagents to selenoxides. When the lesulting selenoxides bear a -hydrogen atom syn elimination giving alkenes occurs readily at room temperature widi formation of selenenic acid by-products (Scheme 13). For allylic selenides, the oxidation does not lead te conjugated... 

Propargyl phenyl selenide is a versatile multifunctional acrylate synthon, as shown in Scheme 12. The (Uanion is prepared and reacted successively with an alkylating agent (R— X) and an electrophile (E ). The oxidative rearrangement of the propargylic selenoxide (35) to an allenic selenenate (36), and thence to the a-phenylselenoenone (37), forms the keystone of this synthetic method, and ovendl yields firom propargyl phenyl selenide are in the range of 38-68%. Further elaboration of (37) is possible... 

As shown in Scheme 1, the reduction of diselenides generates selenols and selenolates, while their oxidation results in the formation of selenenic and seleninic acids and related compounds (see Section 7). Halogenation of diselenides with... 

The partial oxidation of diselenides with appropriate oxidants such as hydrogen peroxide initially generates the corresponding selenenic acids (29) or anhydrides (28). Further oxidation leads to the corresponding seleninic acids (31) or... 

When selenenic acids are generated in the presence of alkenes, addition reactions similar to those of selenenyl halides occur. Oxidation and syn elimination of the adducts (42) provide a convenient synthesis of allylic alcohols (equation... 

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