Silyl lithium

As the phosphonium diylides, lithium phosphonium yldiides, first described by Schlosser and Corey (Ph3P=CR-Li R=H, C3H7) [60-62], have a high nucleophilicity and reactivity. Recently, the a-silylated lithium phosphonium yldiide 20 has been prepared from the stable phosphanyl-(silyl)carbene 19 and alkyl-lithium (Scheme 13). The first crystal X-ray diffraction study of such a reagent was proposed for 20 and its reaction with methyl iodide or phosphorus elec-... 

By analogy, the acetylene aldehyde 500 gives, on addition of the chiral Li-enolate 501 [79-82], the chiral //-lactams 502 and 503 in 75% yield [80-82]. Similar (fhc-tam-forming reactions are discussed elsewhere [70, 83-88]. The ketone 504 affords, with the lithium salt of the silylated lithium amide 505, the Schiff base 506, in 74% yield (Scheme 5.27). The Schiff base 506 is also obtained in 25% yield by heating ketone 504 with (C6H5)3P=N-C6H4Me 507 in boiling toluene for 7 days... 

Tetraalkyl- or tetrasilyltetragallium(I) compounds were also obtained by the reactions of the dioxane adducts of Ga2X4 (X = Cl, Br) with bulky alkyl- or silyllithium compounds [Eq. (5)], which were accompanied by disproportionation of Ga(+2) to Ga(+1) and Ga(+3) [44, 45], In particular the yield of the alkyl derivative 21 was very poor and several unknown byproducts were detected by NMR spectroscopy. Furthermore, the reaction requires the employment of a solvent-free lithium compound, which is not readily available. The reaction of tris(trimethylsilyl)silyl lithium yielded the expected product of the disproportionation [(Me3Si)3Si]2GaCl2Li-(THF)2 besides compound 11. 

Self-condensations are another set of important reactions of organolithium compounds. Tamao and Kawachi had reported that [(tert-butoxy diphenyl)silyl]lithium (20) exhibited ambiphUic character, and underwent a self-condensation reaction to give a [2- tert-butoxy)disilynyl]lithium derivative in THF as shown in Scheme 4, and also a nucleophilic substitution reaction with n-butyllithium . 

SCHEME 4. Self-condensation reaction of [(tert-butoxydiphenyl)silyl]lithium (20) to give [2-(tert-butoxy)disilanyl]hthium derivative 21... 

TRIS(TRIMETHYLSILYL)SILYL LITHIUM TRIS(TETRAHYDROFURAN), LITHIUM TRIS(TRIMETHYLSILYL)SILYLTELLUROLATE BIS(TETRAHYDROFURAN), AND TRIS(TRIMETHYLSILYL)SILYLTELLUROL ... 

Tris(trimethylsilyl)silyl lithium tris(tetrahydrofuran)... 

A. TRIS(TRIMETHYLSILYL)SILYL LITHIUM TRIS(TETRAHYDROFURAN)... 

Alternatively, the reaction may proceed via 1,6-ring closure giving the isolated 2,3-disilanaphthalene 372109. It should be mentioned, however, that under the reaction conditions it is possible that silyl lithium compound 375 formed from the precursor of the silene 376 (obtained from metalation of 377) by a 1,3-trimethylsilyl shift adds to the intermediate silene 371 and that subsequent ring closure with elimination of lithium silanolate gives rise to the observed products 372 and 373 (equation 105). 

Triphenylsilyl zirconium and hafnium derivatives have been prepared from the silyl lithium species. Triphenylsilyl bis(cyclopentadienyl) zirconium chloride undergoes carbonyl insertion under pressure of carbon monoxide (100 psi) to give the corresponding acyl zirconium species which, upon treatment with anhydrous hydrogen chloride in a benzene matrix at —196 °C and warming to room temperature, gives rise to formyl triphenylsilane55. 

A more recent synthetic concept is based on the reaction of diethylamino-sub-stituted silyl-lithium compounds with triflate derivatives of silanes or oligosi-lanes. It leads to stepwise lengthening of Si-Si chains which can be used to assemble polymeric structures [74]. 

Recently silylboronates functionalized on silicon were reported by Suginome and coworkers via the reaction of silyl lithium 379 with borate ester 380 to yield the borosilamide 381. Further transformations on the amine with HC1 furnish the chlorosilane 382, and reaction of SbFs with 382 provide the florosilane 383. The chlorosilanes 382 also react with alcohols or amines to provide the alkoxy or amine substituted silylboronates 384 and 385 respectively (Scheme 61) <20070M1291>. 

Analogous products were obtained from the reaction of silylene 85 with silyl lithium compounds, with alkali metal silylamides and alkali metal alkylamides, and sodium methoxide <2000CC1427, 2004JCD3288, 2005JCD2720, 2005CC5112>. In the case of the reaction with metallated silylamides a thermally initiated rearrangement (114 — 115) to give the new silylamide 115 took place (Scheme 11). 

Hexaphenyldisilane is also obtained in the reaction of triphenylsilane or triphenylmethoxysilane with Na/K alloy after the decomposition of triphenyl-silyl lithium ... 

The effects of additional bonding on the Si—Si framework in reactions of tris(trimethylsilyl)silyl lithium have been investigated by Gilman and Smith219 and no essential differences from triphenylsilyl lithium could be found. 

A l,2-dihydro[l,2]-azasilete derivative has been obtained by treatment of tris(tetrahydrofuran)[tris(trimethylsilyl)-silyl]lithium with 2,6-dimethylbenzoisonitrile (Scheme 24) <1999AGE501, 2002JCD3253>. 

Methods for the reduction of epoxides without introduction of additional functionality are of immense importance. A recent report shows that silyl lithium reagents can be used to reduce keto epoxides <07TL6751>. 

Tris(trimethylsilyl)silyl-magnesiumbromide, made in situ by interaction of tris(trimethylsilyl)silyl-lithium [5] with anhydrous magnesium bromide in ether, reacts with aldehydes and ketones under addition of the magnesium silanide to the C=0 double bond. 

Apart from organic derivatives of pentazene, N5H5, the cyclic compound 78 is, so far, the only other Group IV derivative of this hydride (35). It is formed by the action of ethyl nitrite on the silylated lithium hydrazide 77 in diethyl ether at -78 C [Eq. (99)]. It is a colorless crystalline... 

The silylated lithium ynamine 192 is generated by metaUation with BuLi of 5 -methyl Af-phenyl-trimethylsilylethanimidothioate (190), via a ketenimine intermediate (191), as shown in equation 75. The interconversion between 191 and 192 can be discerned by silylation taking place at both the N- and -positions to afford the Af-silylynamide 193 and the bis(/ -silyl)ketenimine 194. In equation 76 are shown three possible synthetic... 

Summary Methoxy-bis[tris(trimethylsilyl)silyl]methane (4), the first geminal di(hyper-silyl) compound with a central carbon atom, was prepared by the reaction of tris(tri-methylsilyl)silyl lithium with dichloromethyl methyl ether. The structure of 4, which is characterized by considerable distortions due to the spatial demand of the two (MesS aSi groups, is discussed on the basis of an X-ray crystal structure analysis. 

Addition of chlorophosphane to the mixed (silyl)(stannyl)diazo derivative 10 affords the nitrilimine 12 (70 % yield), which was unobtainable using the silylated lithium salt 5, demonstrating the superiority of stannyl diazo compounds over diazolithium salts for the synthesis of stable nitrilimines [13, 14] (Scheme 3). 

Silylation. Lithium enolates of esters and lactones undergo a-silylation with this reagent rather than the more usiial O-silylation encountered with other reagents. Addition of HMPT results in considerable O-silylation. The reagent effects only O-silylation of ketones. 

Jutzi reported the formation of enediol compounds from the reaction of trimethyl-silyl lithium with CO (Eq. (5.51)) [56]. As shown above, they proposed a mechanism involving the dimerization of a lithioxy carbene, which is an acyllithium tautomer (Eq. (5.51)). A similar reaction suggests the possibility of further insertion... 

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