Methyl selenide

Unlike the aryl methyl selenides, the alkyl aryl selenides with alkyl groups of two carbons or more are able to undergo scission of the radical cation at the Cgp-Se bond, yielding the ArSe radical (Fig. 35). This can impact product distribution, particularly under conditions in which water is not present to react with the radical cation. Trends in ease of oxidation typically seen in series of chalcogen compounds can still be observed, and are consistent with trends in the diaryl chalcogenides and aryl methyl chalcogenides. 

On-line anion exchange LC/ICP-MS methods for selenium and chromium speciation have been published [30], In studies of selenium speciation in environmental samples LC/ICP-MS and LC/ ESI-MS methods have been used for the determination of both inorganic and organic selenium species [43]. For the determination of methyl selenide, strong anion exchange and RP chromatography have been employed [43], while for the determination of seleno-aminoacids, IP RP chromatography with on-line detection based on ICP-MS has been successfully employed [44],... 

Lactonization of alkenoyloxy methyl selenides (or iodides) Bu3GeH is generally more effective than Bu3SnH for cyclization of these substrates to y- and 8-lactones. The cyclization (exclusively exo) generally affords cw-fused products. Example ... 

Methyl ethyl selenide, CH3.Se.C2H5, is prepared in a similar manner to the foregoing compound using methyl selenide and ethyl bromide or iodide. It boils at 86° C., has a density of 1 3134 at 23° C., nD 1 4820 at 23° C. 

Phenyl methyl selenide, C6H5.Se.CH3,2 is a pale yellow oil, B.pt. 200° to 201° C., obtained by the action of methyl iodide on sodium phenyl selenide. 

Benzyl methyl selenide,3 (C6H5.CH2)Se(CH3), is prepared from dibenzyl selenide and methyl iodide. Ethyl iodide gives benzyl ethyl selenide, and ethylene dibromide forms dibenzyl ethylene selenide, C2H4(Se.C7H7)2, M.pt. 68° to 69° C., crystallising in pale yellow needles. 

Phenyl methyl selenium dihydroxide, (C6H5)(CH3)Se(OH)2.— The dibromide (10 grams) is triturated with a suspension of 12 grams of silver oxide in 100 c.c. of water until the yellow colour disappears. Filtration, evaporation and desiccation yield about 8 c.c. of the hydroxide as a viscous oil. When heated at 100° C. at 15 mm., or at 170° C. at 760 mm., it decomposes, yielding phenyl methyl selenide, diphenyl diselenide and formaldehyde. The formation of formaldehyde is in agreement with the view that phenyl methyl selenoxide may exist in two isomeric forms, which, being unstable, decompose thus ... 

The methods of synthesis of diaryl and aryl alkyl selenides have been recently reviewed.215 4-Nitro-phenyl methyl selenide was obtained in 93% yield from the reaction of 4-chloronitrobenzene in DMF with a suspension of MeSeLi in THF, prepared from powdered Se and MeLi.216 Other mixed RSeAr selenides were synthesized via alkylation with RI of ArSe resulting from the nucleophilic substitution of unactivated haloarenes ArCl with MeSeLi in DMF at 120 C, followed by MeSe -induced demethyl-ation.217... 

Unsaturated jS-dicarbonylcompounds.2 An attracti ve route to this system involves sclenylation of the enolate of /1-dicarbonyl compounds in the presence of 3-6 equiv. of HMPT, followed by methylation. The resulting methyl selenide is then oxidized by H 202 or m-ClCe.H4.CO3H in CH2C12-H20. 

Another preparative route for synthesis of benzisoselenazol-3(27/)-ones is based on the lithiation of the benzamides, followed by the conversion of dilithium derivatives by direct treatment with selenium, or via 2-[(carbamoyl)phenyl]methyl selenides or 2,2 -bis[(carbamoyl)phenyl] diselenides [167-172], These diselenides are oxidatively cyclized and, depending on the oxidant used, benzisoselenazol-3 (2H)-ones or their 1-oxides are produced in high yields [92, 173],... 

Similarly, 144 has been obtained from the reaction of 1-trimethylsilylcyclopropyl methyl selenide with n-BuLi The a-bromosilane 147 underwent lithiation with n-BuLi in THF at —78 °C to provide 144 with superior efficiency to any other method, Eq. (46))81). 147 was prepared in large quantities by the Hunsdiecker degradation of the 1-trimethylsilylcyclopropanecarboxylic acid 146, obtained by successively reacting the commercially available cyclopropanecarboxylic acid with -BuLi (2 equivalents) and ClSiMe3 82). Uneventfully, 144 added to carbonyl compounds, except for cyclopentanone where enolate anion formation competed the 1-trimethylsilylcyclo-propylcarbinols 148 underwent acid-induced dehydration to the expected 1-trimethyl-silylvinylcyclopropanes 149 79-81) while base induced elimination (KH, diglyme, 90 °C) led to cyclopropylidenecycloalkanes 150 77), Eq. (47). 

Anaerobic reduction of Se04 and SeO to Se° and methylated selenides Selenate and selenite reduction by microorganisms has been noted for some time. Organisms with this capacity include bacteria and fungi (Trudinger et al., 1979 Stolz Oremland, 1999). In bacteria the reductions are mostly a form of anaerobic respiration and result in selenium immobilization with the formation of water-insoluble Se°. In fungi the reductions involve the formation of methylated selenium,... 

The isolable and diermally staUe selenoxides are, dKiefore, rather limited. Stable examples are as follows those derived from selenides which have no hydrogen atoms on the p-carbon, such as dimediyl sel-enide, aryl methyl selenides, diaiyl selenides - and benzyl fdienyl selenides, those with an intramolecular hydrogen bonding, such as (36) and (37), and those leading to an unfavorable double bond such as (38). Vinylic selenoxides (39) and (40) are also generally isolable. 

SYNS NSC-271675 PLATINUM(II), BIS(METHYL SELENIDE)DICHLORO-, cis- PLATINUM, DICHLORO-BIS(METHYL SELENIDE)-, cis- PLATINUM, DICHLOROBIS(SELENOBIS(METHANE))-(SP-4-2)... 

SYNS PLATINUM (H), BIS(METHYL SELENIDE)SCLFATO-, HYDRATE NSC-281278... 

PLATINUM (II), BIS(METHYL SELENIDE)SULFATO-, HYDRATE see SNSlOO PLATINUM BLACK see PJD500 PLATINUM CHLORIDE see PJEOOO PLATINUM(I 0 CHLORIDE see PJE250 PLATINUM COMPOUNDS see PJE500 cis-PLATINUM(II) DIAMMINEDICHLORIDE see PJDOOO... 

Moreover, tram-33 is also obtained in 77% yield on reaction of acetoxymethy] methyl selenide with cyclohcxene in the presence of hydrogen peroxide 7 or on heating cyclohexene with an excess of dimethyl selenoxide in a mixture of acetic acid and chloroform 8. 

Alkyl stannyl selenides are also useful nucleophilic selenium reagents. Tri-methylstannyl or tributylstannyl methyl selenides 58 react with halides 59 to produce unsymmetrical selenides 60 in good yields in the presence of a fluoride ion or by treatment with n-butyllithium (Scheme 44) [84]. Tributylstannyl phenyl selenide (61) reacts smoothly with acetals to give monoselenoacetals 62 in the presence of boron trifluoride etherate (Scheme 45 a) [85]. Similar reaction conditions were applied to the regioselective ring opening of epoxides (Scheme 45b) [86]. 

Scheme 1. Acyl methyl selenides require two equivalents of tin hydride for reduction to the corresponding aldehydes...

Acyl radicals are very useful synthetic intermediates. Their preparation is not simple since the corresponding halides are highly electrophilic and cannot be used as radical precursors. Organocobalt compounds were proposed as suitable source of acyl radicals [44]. However, the use of acyl selenides proved to be more general [45, 46]. These radical precursors can be efficiently prepared from the corresponding carboxylic acids and esters [47]. Acyl phenyl selenides should be preferred, when possible, relative to acyl methyl selenides due to the consumption of two equivalents of tin hydride with this last system (Scheme 1) [4]. Acyl selenides have found many applications in tandem radical additions to alkenes. Examples of intermole-cular [Eq. (18)] [48,49] and intramolecular reactions [Eq. (19)] [50a] are reported. The enoyl selenide 68 give the unsaturated acyl radicals 69. This intermediate... 

Alkyl aryl and dialkyl selenides, aside from the parent compounds methyl phenyl selenide (Scheme 13, a) and trifluoromethylphenyl methyl selenide (Scheme 13, b), cannot be easily metallated. It was expected that the extra stabilization provided by the cyclopropyl group would be sufficient to permit the metallation of cyclopropyl selenides, but that proved not to be the case. ... 

Aryl methyl selenides with the methyl group substituted by an aryl (Scheme 9 and i5),5 .to,72,78,79 vinyl (Schemes a 1-butadienyl (Scheme 17, d) or an ethynyl (Schemes 19 and... 

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