Bis trimethylsilyl Selenide

Synthesis of Bis(trimethylsilyl) Selenide. In the initial studies, bis(trimethylsilyl) selenide was synthesized by the following two methods silylation of sodium selenide (or lithium selenide ) with chlorotrimethylsilane (eq 1) or reaction of bromobenzene, magnesium, and selenium with chlorotrimethylsilane (eq 2).  

However, the former method requires the troublesome manipulation involved in preparing sodium selenide (or lithium selenide) in liquid ammonia and conducting the silylation in benzene (or diethyl ether). The latter method is inefficient and results in a low yield of the desired disilyl selenide. Thus a one-pot, high-yield procedure based on the lithium triethylborohydride reduction of elemental selenium has been developed, as depicted in eq 3. In this method, both preparation of Li2Se and silylation with MesSiCl are performed in THE Technically important is the use of selenium shot if selenium powder is utilized, the yield of Li2Se decreases sharply. Moreover, addition of small amount of boron trifluoride etherate (1.6 mol %) accelerates the silylation of Li2Se.  

Recently it has been reported that the reaction of lithium dis-elenide (Li2Se2) with 2 equiv of chlorotrimethylsilane affords bis(trimethylsilyl) selenide in 73% yield with the concomitant formation of elemental selenium (eq 4).  

Synthesis of Unsymmetrical Selenides. Bis(tiimethylsilyl) selenide reacts with equimolar amounts of n-hutyUithium to generate MesSiSeLi, alkylation of which then provides trimethylsi-lyl alkyl selenides. Similar treatment of Me3SiSeR with BuLi / R X successfully leads to unsymmetrical selenides in good yields (eq 5). Use of acid chlorides in place of alkyl hahdes results in the formation of selenoesters. 

R = alkyl, benzyl, ally , acyl R = alkyl, benzyl 

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Free intermediate thioaldehydes 598 or 602 and the selenoaldehydes 605 and HMDSO 7 are obtained in THF at 0°C on treatment of aliphatic and aromatic aldehydes with bis(trimethylsilyl)thiane 601 or bis(trimethylsilyl)selenide 604 in the presence of traces of butyllithium, while trapping the sensitive intermediate thio- or selenoaldehydes 602 and 605 with cyclopentadiene or cyclohexadiene to furnish mixtures of endo and exo Diels-Alder adducts such as 603 a and 606 a and 603 b and 603 b [148-150], the exo/endo ratio of which can be controlled [150] (Scheme 5.48). Analogous reaction of ketones such as 2-adamantanone or acetylene ketones with MesSiXSiMes 608 (a. X=S (601) b. X=Se (604)) in the presence of... 

CoCl2 6H20 [149] or TMSOTf 20 [150-152] in acetonitrile afford Diels-Alder adducts in yields of up to 85%. The dienals 607 are converted by bis(trimethyl-silyl)thiane 601 or bis(trimethylsilyl)selenide 604 and catalytic amounts of BuLi, via 609, to the intramolecular Diels-Alder products 610 in up to 70% yield [153, 154]. 

In the presence of catalytic amounts of Bp3.0Et2 aromatic aldehydes such as benzaldehyde are converted by bis(trimethylsilyl)selenide 604 into hexamethyldi-siloxane 7 and the corresponding trimers, for example 611 in up to 90% yield. On heating with 1,3-dienes such as 2,3-dimethylbutadiene trimers such as 611 react to give the Diels-Alder product 612 [155] (Scheme 5.49). 

Amides such as DMF or ureas such as N,N-tetramethylurea react with bis(trimethylsilyl)selenide 604 in the presence of BF3-OEt2 to give selenoamides, for example 617, or selenoureas whereas esters such as n-butyl benzoate react with 604 in the presence of Bp3-Et20 and 2,3-dimethylbutadiene to give 619 via 618 [157]. On heating with P4Sio/sulfur and hexamethyldisiloxane 7 y9-ketoesters such as ethyl acetoacetate are converted to 3H-l,2-dithiole-3-thiones such as 620 in high yields [158] (Scheme 5.51 cf. also Section 8.6). 

A. HEXAMETHYLD1SILASELENANE AND HEXAMETHYLDISILATEL-LURANE, [ BIS (TRIMETHYLSILYL) SELENIDE AND BIS (TRIMETHYLSILYL) TELLURIDE]... 

Bis(trimethylsilyl) selenide (mp -7°, bp 58-59°/ll torr)14 and bis(trimethyl-silyl) telluride (mp 13.5°, bp 74°/11 torr)14 are liquids of low volatility with revolting and persistent odors resembling garlic and rotten cabbage. They exhibit first-order H nmr spectra 2,3 [(CH3)3Si]2Se 5(CH3) 0.43 ppm,/(H—13C)... 

Bis(trimethylsilyl)selenide (54) [80] is another useful reagent as a source of a nucleophilic selenium species. This reagent has been shown to be useful for a convenient one-pot synthesis of unsymmetrical selenides 55 by stepwise treatment with u-butyllithium and the corresponding halides (Scheme 41) [81]. 

Early attempts to prepare selenoaldehydes by treatment of aldehydes with H2Se under acidic conditions yielded oligomeric or polymeric sele-nides, possibly via self-condensation of selenoaldehydes [15JPR116 67JCS(B)117]. In 1988, Japanese workers reported that the reaction of aldehydes with bis(trimethylsilyl)selenide in the presence of a catalytic quantity of butyl lithium afforded selenoaldehydes (88JA1976). This novel method has been exploited for the first intramolecular Diels-Alder reactions of selenoaldehydes (88TL6965). Dienal (79) was converted into dienselenal (80) and then into a mixture of stereoisomeric adducts 81 and 82. The major product was as-fused isomer 81, derived from the endo transition state. These results compare favorably with intramolecular thio-aldehyde reactions (Section II,B). 

The cyclotrimerization of selenoaldehydes is reversible <82ZAAC(488)99>. Thus, when aldehydes react with bis(trimethylsilyl)selenide in the presence of boron trifluoride etherate, triselenanes (120) are produced. These can be used as sources of selenoaldehydes, which undergo cycloaddition with... 

Heterodiene synthesis. Bis(trimethylsilyl) selenide in toluene treated under argon with ca. 2 eqs. dimethylaluminium chloride in hexane, stirred for 15 h at 100°, the solvent removed carefully under reduced pressure, THF, cyclopentadiene, and fluorenone added sequentially to the residue, and heated under reflux for 16h - cycloadduct. Y 77%. The method is also applicable to the in 5//w-generation of simple dialkyl selenoketones. F.e.s. M. Segi et al.. Tetrahedron Letters 30, 2095-8 (1989). 

Bis (trimethylsilyl) selenide s. under BuLi Tris( trimethylsilyl) phosphine... 

Direct conversion of aldehydes to selenoaldehydes has been achieved by treatment with bis(trimethylsilyl) selenide in the presence of a catalytic amount of butyUithium (eq 6). ... 

Bis(trimethylsilyl) selenide is useful as a two-electron reducing agent for the reduction of sulfoxides, selenoxides, and telluroxides to corresponding sulfides, selenides, and tellurides, respectively (eq 8). ... 

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