Anions selenolate

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... 

Ono and Kamimura have found a very simple method for the stereo-control of the Michael addition of thiols, selenols, or alcohols. The Michael addition of thiolate anions to nitroalkenes followed by protonation at -78 °C gives anti-(J-nitro sulfides (Eq. 4.8).11 This procedure can be extended to the preparation of a/jti-(3-nitro selenides (Eq. 4.9)12 and a/jti-(3-nitro ethers (Eq. 4.10).13 The addition products of benzyl alcohol are converted into P-amino alcohols with the retention of the configuration, which is a useful method for anri-P-amino alcohols. This is an alternative method of stereoselective nitro-aldol reactions (Section 3.3). The anti selectivity of these reactions is explained on the basis of stereoselective protonation to nitronate anion intermediates. The high stereoselectivity requires heteroatom substituents on the P-position of the nitro group. The computational calculation exhibits that the heteroatom covers one site of the plane of the nitronate anion.14... 

The SSPs are prepared by the reaction of a stabilized Cu(I) cation, with an indium(III) or gallium(III) chalcogenide anion, prepared in situ by reaction of the conjugate acid of the thiol or selenol with NaOMe in methanol (Scheme 6.1 below).1,3... 

Selenoprotein A is remarkably heat stable, as seen by the loss of only 20% of activity on boiling at pH 8.0 for lOmin (Thrner and Stadtman 1973). Although selenoprotein A contains one tyrosine and no tryptophan residues, it contains six phenylalanine residues and thus has an unusual absorbance spectrum (Cone et al. 1977). Upon reduction, a unique absorption peak emerges at 238 nm, presumably due to the ionized selenol of selenocysteine, which is not present in the oxidized enzyme. The activity of selenoprotein A was initially measured as its ability to complement fractions B and C for production of acetate from glycine, in the presence of reducing equivalents (e.g., dithiothreitol). Numerous purification schemes were adopted for isolation of selenoprotein A, all of which employed the use of an anion exchange column to exploit the strongly acidic character of the protein. 

The strong nucleophilicity of aryl thiolate and aryl selenolate anions of tetraphenylphos-... 

Reactions of 2-(3-hydroxy-3-phenylpropylseleno)benzoxazole with KH in tetrahydrofuran (THF) give selenetane 31. In the cases of /< rt-alcohols (R1 = C2H5 or CH2Ph), complex mixtures of products and no expected selenetane 31 are obtained because of steric hindrance at the reaction site. The formation of a selenetane is explained by a spiro intermediate which is converted into a selenolate anion. Intramolecular displacement of 30 gives the selenetane 31 (Scheme 7) <1998H633>. 

Various reducing agents have been used for the generation of selenolates from diselenides or selenocyanates. Alkali metals M (M = Li, Na, K)149,150 or alkali hydrides MH (M = Li, Na, K)151,152 can generate the corresponding selenolate anions such as 80 these are more reactive than the borane complexes of type 77 (Scheme 15). Diaryl diselenides are easier reduced than dialkyl diselenides, but the mechanism for the reduction of selenocyanates is complex and can lead to either diselenides or selenolates.153,154... 

Disodium tellurapentathionate, tetraphenylarsonium chloride, and sodium 2,2-dicyano-ethene-l-thiolate-l-selenolate in aqueous methanol produced an anionic tellurium complex with two ligand molecules coordinated to tellurium2. 

Selenides and selenolate anions are usually less basic and more nucleophilic than corresponding sulfur compounds. This unique property was recognized in 1973 by Sharpless and Lauer and used for the conversion of epoxides into allylic alcohols [18]. This publication can be regarded as another milestone in organoselenium chemistry. New aspects and a variety of other related reactions are summarized by M. Iwaoka and S. Tomoda in Chap. 3. 

Anionic cycloaddition reactions of a,j8-unsaturated selenolates and tellurolates in the synthesis of selenophene, tellurophene, and 1,3,4-sele-nadiazine derivatives 87UK267. 

The analogy between phenyl thiolate (Ph-S ) and ferrocenyl thiolate (Fc-S ) anions leads to the expectation that many compounds containing ferrocenyl thiolate units as either substituents or ligands should exist. This is indeed the case and, although with fewer examples, is also true for ferrocenyl selenolate and tellurolate. Similarly, l,T-ferrocenylene dithiolate compounds (which correspond to o-phenylene dithio-lates) are known, together with the analogous l,r-ferrocenylene diselenolates and ditellurolates. 

Nucleophilic displacement at a terminal methylidyne ligand, with regeneration of a metal - carbon triple bond in 199 (E = S or Se, R = Me, Ph, or P-NO2QH4) to form a new methylidyne ligand, occurs in the reaction of 198 [L = HB(3,5-Mc2—C3HN2)3] with thiolate or selenolate anions under phase-transfer conditions 149). 

The yields in this type of synthesis are generally better than 90% (based on dissolved anode material) and the isolated material is of high purity (55). Anionic species [Cu(SR) ] " with n > 1 are generally not isolated and both copper alkyl- and arenethiolates are accessible in this way. Moreover, this technique also allows access to copper selenolates [Cu(SeR)] (57). 

Nucleophilic attack of selenolate anions on the iminium ion complex, generated... 

Selenolates such as Na2Se, NaSeH, PhSeNa, etc., and tellurolates such as NapTe, NaTeH, PhTeNa, etc., are excellent nucleophiles and can reduce a variety of functional groups by nucleophilic attack or single electron-transfer. On treatment with alkali metal selenolates (or amine salts of HpSe and PhSeH), reduction or reductive selenation of ketones and aldehydes, C=C reduction of a,/l-unsaturated compounds, and reduction of nitrogen compounds such as nitro compounds occur successfully [118, 176]. Compared with these selenolate anions, the corresponding tellurium compounds are highly reactive not only toward the same substrates but also toward halo compounds such as a-bromo ketones and vic-dibromoalkanes [46, 52, 177]. 

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