Sodium phenylselenoate

Sodium phenylseleno(triethoxy)borate, Na [QH5SeB(OC2H,),] (1), 14, 284. 

Miyashita M, Hoshino M, Yoshikoshi A (1988) Sodium Phenylseleno(triethoxy)borate, Na [PhSeB(OEt)3]7 the Reactive Species Generated from (PhSe)2 with NaBlT) in Ethanol. Tetrahedron Lett 29 347... 

The reaction with a, -epoxy carbonyl compounds 12 leads to the corresponding reductive ring-opened products, -hydroxy carbonyl compounds 13, in good yields (Scheme 22). Electrochemically generated benzeneselenolate [21,22] and sodium phenylseleno(triethoxy)borate (1) [35, 36], have been applied for this type of reaction as a nucleophilic selenolate. In the latter case, the reaction mechanism was suggested as shown in Scheme 23 [36]. Reaction of 1 with 12 first produces the ring-opened adduct 14, which is then reacted with an excess amount of 1 to produce the final product 13. This method is important as a simple synthetic procedure to aldols and -hydroxy esters that are rather difficult to obtain by other methods. The reactions have been extended to the reduction of more functionalized a, -epoxy carbonyl compounds [37] and have been successfully applied for the synthesis of several natural products [38]. 

Benzeneselenol, a representative selenol, is a colorless liquid of greater acidity than benzenefhiol [pK = 5.9 (PhSeH) 6.5 (PhSH)]. Benzeneselenol is usually synfhesized by the reaction of phenylmagnesium bromide with metallic selenium then quenching wifh aqueous hydrochloric acid [10]. Similar hydrolysis of the sodium phenylseleno(triethoxy)borate complex prepared by fhe reduction of diphenyl diselenide wifh sodium borohydride is a convenient alternative [11]. 

Sodium phenylselenoate has been used to convert primary lactones into the corresponding w-olefinic esters (Scheme 7)." Other synthetically useful elimina-... 

Sodium phenylseleno(triethoxy)borate p-Hydroxyketones from a,p-oxidoketones... 

Treatment of tetrahydroberberine (26) with sodium benzenethiolate (48) or -selenolate (49) in the presence of ruthenium catalyst afforded the C-14—N bond cleavage products 51 or 52 with a phenylthio or phenylseleno group at C-14 (Scheme 12). The latter was converted to the 10-membered amino olefin 53 on treatment with m-chloroperbenzoic acid. 

Method B. Typical procedure. A mixture of elemental tellurium (0.127 g, 1 mmol) and sodium hydride (0.0528 g 2.2 mmol) in dimethylformamide (3 mL) was heated at 140°C under nitrogen and magnetic stirring for 1 h. The resulting violet solution was cooled to 0°C in an ice bath and treated dropwise with a solution of ethyl a-(phenylseleno) mesityl acetate (0.361 g, 1 mmol) in DML (2 mL). A vigorous reaction occurred and the colour of the solution changed from violet to dark brown. After the addition the mixture was diluted... 

Precursor y-halogeno alcohols are frequently prepared by the classic sequence of addition of hydrogen halide to a,/3-unsaturated aldehydes, ketones, acids or esters, followed by Grignard reaction or hydride reduction. Recently a novel and general synthesis of 3-methoxyoxetanes from 3-phenylseleno-2-propenal was reported. This method comprises a sequence of Grignard addition to the aldehyde function, treatment with two equivalents of MCPBA, and then reaction with methanolic sodium hydroxide (equation 78) (80JOC4063). 

DIB in combination with sodium azide and diphenyl disulphide or diphenyl diselenide can replace the methinic hydrogen of aliphatic, aromatic and heteroaromatic aldehydes by the phenylthio or phenylseleno group. The corresponding esters were obtained in moderate (for unsaturated aldehydes) to very good yields [109] ... 

Reversal of phenylseleno cyclizations. Sodium in liquid ammonia reacts with phenylselenolactones and ethers to give olefinic products in good yield. ... 

Epoxide cleavage, Sodium selenophenolate reacts with the furanose 1, prepared from D-glucose, to form the diselenide 3 in quantitative yield. This reaction involves formation and cleavage of the epoxide 2, which can be also prepared by treatment of 1 with NaH. The epoxide is cleaved regiospecifically by attack from the less hindered side at C4. The phenylseleno group can be removed reductively by Raney nickel. The product was used to prepare isoepiallomuscarine (5). 

Cyclohexene is converted to tnmv-1-(4-mcthylphcnylsulfonylamino)-2-(phenylseleno)cyclohexane (59) by treatment with diphenyl diselenide and chloramine-T, followed by reductive workup with sodium borohydride66. The intermediate product A formed from diselenide and chlor-amine-T is believed to play the role of an electrophile attacking the alkene. 

One of the most important addition reactions which involves nitrogen nucleophiles is the azidoselenenylation of alkenes because both the azido and the phenylseleno group can give rise to several useful transformations. These compounds were first prepared by Krief from the reaction of alkenes with PhSeBr followed by sodium azide in DMF [54]. Direct azidoselenenylation of alkenes can be effected with PhSeCl and sodium azide in DMSO [55]. Under these conditions the reaction is stereospecific but it is not regiospecific. Similarly, the reaction of exocyclic alkenes with N-(phenylseleno)phthalimide and azido-trimethylsilane in methylene chloride (Scheme 11) gives rise to a 1 1 mixture of the regioisomers 67 and 68 [56]. 

The best experimental conditions to introduce a phenylseleno and an azido group to the alkene double bond are those which employ diphenyl diselenide, sodium azide and iodobenzene diacetate in methylene chloride. Under these conditions, however, the addition reaction occurs through the radical mechanism illustrated in Scheme 12 [581. The addition therefore occurs with an anti Markovnikov orientation and it is not stereospecific. The reaction is initiated by the oxidation of the azido anion to the azido radical, which adds to the alkene to afford a carbon radical. This is trapped by the PhSeSePh to afford the final product and a PhSe radical, which dimerizes to give the diselenide. 

Phenyl Phenylseleno Tellurium 0.79 g (5 mmol) of benzeneselenol are dissolved in 5ml of anhydrous tetrahydrofuran. Under nitrogen, 2.6 ml of 2 molar ethyl magnesium bromide (5.2 mmol) in diethyl ether are added, the mixture is heated under reflux for 2 h, cooled to 0°, and a solution of phenyl tellurium bromide, prepared from 1.02 g (2.5 mmol) of diphenyl ditellurium and 0.40 g (2.5 mmol) of bromine in tetrahydro-furan/benzene, is added. The reaction mixture is then warmed to 20°. stirred at 20" for 30 min, then 40 ml of low-boiling petroleum ether followed by aqueous ammonium chloride solution are added. The organic layer is separated, washed with saturated aqueous sodium chloride, dried with anhydrous magnesium sulfate, filtered, and evaporated. The residue (1.38g) is plaeed on a eolumn containing 120g of silica gel G, the product (Rf 0.60) is eluted with petroleum ether, the eluate is evaporated, and reddish needles are obtained yield 1.13 g (63%) m.p, 48° (petroleum ether). 

P-Hydroxy selenides are conveniently prepared from epoxides by treatment with sodium phenylse-lenide (Scheme 32) and by the addition of benzeneselenenic acid and its derivatives to alkenes (Scheme 33), - -" although in some cases these reactions are not regioselective. Useful phenylseleno -etherification and -lactonization reactions have been developed which can be regioselective (equation 42 and Schemes 34 and 35). -" " Selenide- and selenoxide-stabilized carbanions have been used in addition reactions with aldehydes and ketones, - and the reduction of a-seleno ketones also provides a route to P-hydroxy selenides. ... 

Diethyl l-(phenylseleno)- and l-(phenyltelluro)methylphosphonates " have been prepared in 77-92% yields by the reaction of diethyl iodomethylphosphonate with sodium phenylselenide and lithium phenylteUuride, respectively. 

Sodium borohydride-aqueous base. Enone reduction. 2,6-Di-t-butyl- Formation of aryl radicals. Redn intermediates. Addition to a side-chain 6 Organotelluride anions. Ditellun are useful for phenylseleno removal front... 

Phenylselenofluoration of acetylenes 359 (R = Pr or Bu) to give 360 is accomplished by the joint action of A-(phenylseleno)phthalimide and EtsN-SHF. Free-radical selenosulphonation of conjugated enynes by PhSeTos under photochemical conditions or in the presence of azoisobutyronitrile yields mixtures of stereoisomers, e.g. equation The action of / -methoxyphenyltellurium trichloride on terminal alkynes RC=CH (R = cyclohexyl, HOCH2 or Ar) results in cw-adducts 361 (Ar = -MeOC6H4) 48 Sodium benzenetellurolate, PhTeNa, formed in situ from diphenyl ditelluride and sodium borohy-... 

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