Selenoxides oxidations with

Diphenyl selenoxide Oxidations with selenoxides Oxidative dimerization... 

Oxidation of thiols and related compounds with organoselenium(IV) and organotellurium(rV) compounds 102 Other oxidations with selenoxides and telluroxides 106 Thiolperoxidase and haloperoxidase-like activity of organoselenides and organotellurides 108... 

The S- and Se-(perfluoroalkyl)dibenzothiophenium salts 17-27 were synthesized according to three methods (Eq. 4) (1) fluorination of the corresponding sulfide 1-6 or 8 or selenide 11 or 12 with F2 in the presence of an acid or a Lewis acid (2) fluorination with F2, followed by treatment with an acid or a Lewis acid and (3) treatment of sulfoxide 13, 14, or 15 or selenoxide 16 with triflic anhydride (Tf20). Sulfoxides 13-15 and selenoxide 16 were prepared by oxidation of the corresponding sulfides or selenide with m-chloroperbenzoic acid. 

Furukawa, N. Ogawa, S. Matsumura, K. Fuji-hara, H. Extremely facile ligand-exchange and disproportionation reactions of diaryl sulfoxides, selenoxides, and triarylphosphine oxides with organolithium and Grignard reagents. 

Cyclohexyl selenides 162 can be prepared from the 4-substituted cyclohexanones via the selenoketals and upon oxidation with chiral oxidants, compounds 163 were obtained in high yields and with excellent stereoselectivities. Some representative examples are summarized in Table 5 and it is obvious that only the Davies oxidant 158 is leading to high enantiomeric excesses in the product 163 whereas under Sharpless oxidation conditions no selectivity is obtained. The titanium complex formed in the Sharpless oxidant may promote the racemization of the intermediate selenoxide by acting as a Lewis acid catalyst, while the aprotic nature of the Davies oxidant 158 slows down racemization dramatically. 

The [2,3]sigmatropic rearrangement of allylic selenides has proven to be a useful method for the preparation of allenic alcohols. Selenide 170 was obtained by a free-radical selenosulfonation of the corresponding enyne. Oxidation with mCPBA afforded the allenic alcohol 171 in 89% yield via an intermediate selenoxide (Scheme 49).295... 

Several different functional groups can be introduced by selenenylation. The benzeneselenenyl ion tolerates a wide range of anionic groups. However, with differing anionic moieties the reactivity of the benzeneselenenyl ion varies greatly. All adducts can be subsequently converted to either allylic or vinylic moieties by the syn elimination of the corresponding selenoxide (oxidized selenide). 

J.l Oxidation with Dimethyl Sulfoxide 4.422 Oxidation with Selenoxides... 

Entries 1 and 2 in Table 8 are examples of an overall antarafacial 1,3-transposition of a hydroxy group by selenium compounds20,21. Treatment of the alcohols with 2-nitrophenyl seleno-cyanate in the presence of tributylphosphine gave the selenide with inversion of configuration. Oxidation with hydrogen peroxide led to the selenoxide, which rearranged suprafacially to the allylic alcohol. 

Thus, when cyclohexyl selenides 1, prepared from the corresponding 4-sub-stituted cyclohexanone via the selenoketals, were oxidized with various Davis and Sharpless oxidants, the chiral alkyl aryl 4-substituted cyclohexylidenemethyl ketones were obtained in excellent chemical yields with high enantiomeric excesses. Typical results are summarized in Table 4. In this asymmetric induction, of the substrate and the chiral oxidant employed were revealed to show a remarkable effect upon the enantioselectivity of the product. The use of a methyl moiety as instead of a phenyl moiety gave a higher ee value, probably due to the steric difference between the two groups bonded to the selenium atom of the substrate. The results indicate that the titanium complex of the Sharpless oxidant may promote the racemization of the chiral selenoxide intermediate by acting as a Lewis acid catalyst, whereas the racemization in the case of the Davis oxidant, which is aprotic in nature, is slow. 

Isoxazole-supported selenium resins, produced via 1,3-dipolar cycloaddition of nitrile oxides with propargyl selenium resin, were subjected to a-alkylation reactions with various electrophiles, leading to 3-aryl-5-i4-substituted ethenylisoxazoles in satisfactory yields (62-78%) and purity (90-99%). Compound 238 gave olefin 240, through selenoxide elimination from the a-alkylation product 239 (Scheme 56) <2003OL4649>. 

Sodium periodate (sodium metaperiodate), NaI04 (mp 300 °C dec), which is commercially available, is applied mainly in aqueous or aqueous-alcoholic solutions. Like the free periodic acid, sodium periodate cleaves vicinal diols to carbonyl compounds [762], This reaction is especially useful in connection with potassium permanganate [763, 764] or osmium tetroxide [765], Such mixed oxidants oxidize alkenes to carbonyl compounds or carboxylic acids, evidently by way of vicinal diols as intermediates. Sulfides are transformed by sodium periodate into sulfoxides [322, 323, 766, 767, 768, 769, 770, 771, 772], and selenides are converted into selenoxides [773]. Sodium periodate is also a reoxidant of lower valency ruthenium in oxidations with ruthenium tetroxide [567, 774],... 

Diphenyl selenide is oxidized with peroxyacetic acid at room temperature to diphenyl selenoxide hydrate, C6H5Se(OH)2, in 43% yield after 2 h [1198]. Benzyl phenyl selenide is oxidized to benzyl phenyl selenoxide by sodium periodate in aqueous methanol at 0 °C in 95% yield and by iodobenzene dichloride in aqueous pyridine at -40 °C in 85% yield [773]. 

A stereoreversed cyclobutanone formation was realized starting from oxaspiropentanes by using the selenoxide function as a leaving group. Treating oxaspiropentanes 94 with sodium benzeneselenolate in ethanol affords j8-hydroxy selenides 95 which, on oxidation with 3-chloro-peroxybenzoic acid at — 78 to — 30 °C, led directly to the corresponding cyclobutanones 96 (Table 3). The stereochemistry in this reaction is opposite to that normally observed in the acid-catalyzed rearrangement of oxaspiropentanes. 

The selenium version of this reaction offers the advantages that over-oxidation is no problem and that the elimination of the selenoxides occurs at room temperature or below so that the oxidation and elimination normally occur as a single step.23 A simple example is the preparation of another starting material 158 for a dienone-phenol rearrangement.24 The lithium enolate of spirocyclic ketone 155 reacts with PhSeCl to give 156 and oxidation with H202 gives the dienone 158 directly, with the selenoxide 157 as an intermediate. The overall yield is 83%. 

The congeneric 0-acyl esters of iV-hydroxypyridine-2-selenone can also be prepared since the corresponding selenohydroxamic acid is readily available by treatment of 2-bromopyridine-iV-oxide with sodium borohydride and selenium. As shown in Scheme 11, this variant of the decarboxylative rearrangement, when followed by ozonolysis and subsequent selenoxide elimination, provided a useful route to optically pure L-vinylglycine from a protected glutamic acid derivative [16]. 

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