Selenides selenoxides

The 7 a-bromo steroid (9) can also be treated with sodium phenyl selenolate (41). The resultant 7 P-phenyl selenide (13) can be oxidized and the corresponding phenyl selenoxide elirninated to form the 7-dehydtocholesteryl ester (11). 

A -methyl-5//,7//-dibenzo[d,.g][l,5]telluroazocine 65, its thiooxide 67a (X=S, R= Me) (95JA6388). The same type of reaction with benzylamine and sodium selenide gives A-benzyl-5//,7//-dibenzo[d,g][l,5]telluroazocine selenoxide 67b (X = Se, R = CH2Ph). Reaction of the tellurium dibromide 66 with sodium sulfide carried out in the absence of the primary amines affords the eight-member Te,S-containing heterocycle 5//,7//-dibenzo[d,g][l,5]telluroazocine (92CL151). 

The stmcture of the compound 67b was determined by X-ray (95JA6388). The length of the Te=Se bond (2.445 A) is 0.1 A shorter that in bis(2-ethylcarboxy-phenyltellurenyl) selenide (81CSC1353), which points to a greater double bond character of this bond in the former compound. Selenoxide 67b has a boat conformation. The length of the transannular Te- N bond (2.620 A) is appreciably shorter than the corresponding van der Waals contact (3.70 A). The intramolecular coordination Te- N bond thus formed contributes to the stabilization of the boat conformation of the compounds 67. 

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. ... 

A 30% solution of hydrogen peroxide in water was purchased from Mallinckrodt Chemical Works. The reaction requires 2 molar equivalents of hydrogen peroxide, the first to oxidize the selenide to the selenoxide and the second to oxidize the elimination product, benzeneselenenic acid, to benzeneseleninic acid. The submitters recommend that the hydrogen peroxide solution be taken from a recently opened bottle, or titrated to verify its concentration. 

Selenoxides are even more reactive than sulfoxides toward (3-elimination. In fact, many selenoxides react spontaneously when generated at room temperature. Synthetic procedures based on selenoxide eliminations usually involve synthesis of the corresponding selenide followed by oxidation and in situ elimination. We have already discussed examples of these procedures in Section 4.3.2, where the conversion of ketones and esters to their a, (3-unsaturated derivatives is considered. Selenides can... 

The selenides prepared by any of these methods can be converted to selenoxides by such oxidants as hydrogen peroxide, sodium metaperiodate, peroxycarboxylic acids, 1-butyl hydroperoxide, or ozone. 

The organic substrates in Chart 8 can be divided into two main categories in which (i) the oxidation of olefins, sulfides, and selenides involves oxygen atom transfer to yield epoxides, sulfoxides, and selenoxides, respectively, whereas (ii) the oxidation of hydroquinones and quinone dioximes formally involves loss of two electrons and two protons to yield quinones and dinitrosobenzenes, respectively. In order to provide a unifying mechanistic theme for the seemingly disparate transformations in Chart 8, we note that nitrogen dioxide exists in equilibrium with its dimeric forms, namely, the predominant N—N bonded dimer 02N—N02 and the minor N—O bonded isomer ONO—N02 (equation 88). 

The reagent also converts sulfoxides and selenoxides into sulfides and selenides, respectively, but does not reduce amine oxides. 

Epoxyketone 60 has also been prepared by hydroxyselenation of 4-acetyl-1-methylcyclohexene with phenylselenium chloride and water, oxidation of the selenide to selenoxide with buffered aqueous oxone, and elimination of the se-lenoxide in the same pot to provide the epoxide [80]. Control of the conditions was essential to prevent epimerization of the ketone. This route has little to recommend it given the expense and toxicity of the reagents, the moderate yield, and the problems with epimerization. 

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. 

Allylic alcohols can also be obtained from epoxides by ring opening with a selenide anion followed by elimination via the selenoxide (see Section 6.8.3 for discussion of selenoxide elimination). The elimination occurs regiospecifically away from the hydroxy group.116 117 118... 

Oxidation of chiral sulfonimines (R"S02N=CHAr)and chiral sulfamyl-imines (R RNS02N=CHAr)affords optically active 2-sulfonyloxaziridines and 2-sulfamyloxaziridines, respectively. These chiral, oxidizing reagents have been used in the asymmetric oxidation of sulfides to sulfoxides (15-68% ee), 11-13 selenides to selenoxides (8-9% ee] enolates to a-hydroxycarbonyl compounds (8-37% ee) and in the asymmetric epoxidation of alkenes (15-40% ee)... 

Formation of CK-configurated cyclobutanones has also been observed with 2-methylcyclopen-tanone and 2-methylcyclohexanone/8 However, stereoreversed eyclobutanone formation can be achieved by opening the intermediate oxaspiropentane with sodium phenyl selenide, oxidation of the resulting / -hydroxy selenide with 3-chloroperoxybenzoic acid and subsequent rearrangement in the presence of pyridine/18 Thus, from one oxaspiropentane 8, either stereoisomeric eyclobutanone cis- or lrans-9 was produced. The stereoreversed eyclobutanone formation proceeds from a stereohomogenous / -hydroxy selenoxide and is thought to be conformationally controlled. 

Utilizing selenoxide syn elimination as the key step, a two-step procedure has been developed for the conversion of ketones to enones.22 Cyclobutyl phenyl ketone (52) and 3-phenylcyclobu-tanone (55) were both transformed via the phenyl selenides to the corresponding 1-cyclobutenyl phenyl ketone and 3-phenyIcyclobut-2-en-l-one in 74 and 26% overall yield, respectively.22... 

Several cyclobutenes can be synthesized by elimination of selenoxides from the corresponding methyl- or phenylselanyl derivatives 58 or by elimination of dimethyl selenide from the corresponding selenonium salts 60. The results of these conversions are summarized in Table l.23 The cyclobutenes have been used as precursors for substituted butadienes.23... 

Dibenzoselenophene has been obtained by the sodamide promoted cyclization of diphenyl selenoxide (153) (34CR(l99)53l), and via diazotization of o-aminodiphenyl selenide (154) (39JCS151). 

Selenides (290) and (292) were oxidized to the unstable selenoxides (298) and (299) by aqueous hydrogen peroxide under controlled conditions or by sodium metaperiodate. When selenoxide (298) was subjected to the Pummerer reaction using acetic anhydride in the presence of N- phenylmaleimide, a mixture of exo/endo adducts (144) was obtained in 58% yield, indicating the transient formation of the selenolo[3,4-c]thiophene (143 Scheme 100) <77H(6)1349). 

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