Lithium -Trimethylchlorosilane

Lithium-Trimethylchlorosilane, 323 Lithium aoetylide, 324-325 Lithium alkynides, 189 ... 

To absolution of 1.00 mol of ethyl lithium in 800-900 ml of diethyl ether (see Chapter II, Exp. 1) was added, with cooling between -20 and -10°C, 0.50 nol of dry propargyl alcohol, dissolved in 100 ml of diethyl ether. Subsequently 1.1 mol of trimethylchlorosilane was introduced over a period of 25 min with cooling between -15 and +5°C. After stirring for an additional 2 h at about 30°C the suspension was poured into a solution of 30 g of acetic acid in 150 ml of water. After stirring for 1 h at room temperature the layers were separated and the aqueous layer v/as extracted four times with diethyl ether. The combined ethereal solutions were washed with sodium hydrogen carbonate solution in order to neutralize acetic acid, and were then dried over magnesium sulfate. The diethyl ether was removed by evaporation in a water-pump vacuum and the residue distilled... 

Intramolecular cyclization of 2-phenysulfonylmethyl lactam 3 took place upon reaction with lithium hexamethyldisilazan via generating its a-sulfonyl carbanion to give a cyclized postulated intermediate that can be quenched with trimethylchlorosilane to afford the stable silyl ketal 4. The later ketal was desulfonylated by Raney-Ni and desilylated through treatment with tetrabutyl ammonium fluoride (BU4NF) to afford the carbacephem 5 (94M71) (Scheme 1). 

Caution. Tetrahydrofuran is extremely flammable and forms explosive peroxides only freshly distilled, peroxide-free material should be used. Lithium-dispersion is a hazardous material and must be handled in dry conditions and under an inert gas atmosphere. Trimethylchlorosilane and trichloromethylsilane can cause severe skin and eye burns. All manipulations should be carried out in a well-ventilated fume hood protective gloves and safety glasses should be worn. 

In a rather more unusual process, presumably involving tellurium-lithium exchange, acyl tellurides may be converted into silyl enol ethers of acyl silanes by treatment with butyl lithium and trimethylchlorosilane. In this procedure it is the Z isomer which is the predominant product (Scheme 24)100. 

During reactions of 202 with an equivalent amount of lithium or potassium, the reaction mixture became a yellow suspension which, when reacted with trimethylchlorosilane, gave... 

A variation of the preparative method for octamethyltrisilane (XIII n=3) involves the reaction of dimethyldichlorosilane with lithium in the presence of a large excess of trimethylchlorosilane in tetrahydrofuran (60). The yields of the trisilane are good ( 65%), and small amounts of the next two higher homologs also are obtained. An advantage claimed for this procedure is that it is a one-step synthesis employing commercially available materials. 

A highly branched-chain permethylated polysilane, tetrakis(trimethyl-silyl)silane, can be prepared in 70% yield by a mixed lithium coupling of trimethylchlorosilane (20% molar excess) and silicon tetrachloride in tetrahydrofuran (63). 

The use of lithium tetramethylpiperidide (LiTMP) as the base, followed by a quench with trimethylchlorosilane, has been shown to effectively silylate iV,iV-d i meth y I amides. With two equivalents of base the reaction occurs on the same methyl group, probably because the first trimethylsilyl group favors the formation of and stabilizes the anion on the same carbon atom.136 137 The process has been extended to thiobenzamide136 and aliphatic amides.137... 

The strategy of incorporating silicon as a reactive component in the polymeric system to attain flame retardancy has been explored. For example, Ebdon et al. carried out silylation to the polystyrene using //-butyl lithium in the presence of tetramethylethylenediamine, followed by reaction with trimethylchlorosilane, dichlorodimethylsilane, or trichloromethylsilane, as shown in Scheme 8.1. Poly(vinyl alcohol) films have also been modified with chlorosilanes (Scheme 8.1). 

Trimethylsilyl cyanide has been prepared in modest yield by the action of hexamethyldisilazane on hydrogen cyanide8 and the reaction of silver cyanide with trimethylchlorosilane.6,7 It has been prepared in good yield by the treatment of preformed lithium cyanide (from LiH and HCN) with trimethylchlorosilane in ether.7 The procedure described here not only affords trimethylsilyl cyanide in good yield, but also avoids the use of hydrogen cyanide and the need for Schlenk ware. 

The stereoselective reaction of lithium isodicyclopentadienide (50) with methyl iodide and trimethylchlorosilane shows an amazing dependency on temperature. Electrophilic attack at the endo face occurs at —78 °C in THF, whereas 50 is attacked from the exo face at room temperature (Figure 15)84. 

Wurtz coupling reactions of chlorosilanes are the main route to the silicon-silicon bonded compounds. For example, hexamethyldisilane can be prepared by refluxing trimethylchlorosilane with lithium sand in THF (97%). Lithium may be substituted by sodium by using a mixture of HMPA-THF as the solvent. Linear and branched oligosilanes can be prepared by the same method (equations 55-57). 

The 1,4-dihydropyrazine system has been prepared by reductive silylation of pyrazine with alkali metals and halogenosilanes. Thus pyrazine with lithium and trimethylchlorosilane gives l,4-bis(trimethylsilyl)-l,4-dihydropyrazine (623). Reduction of pyrazine with sodium in ethanol gives piperazine (22). 

The reaction of the lithium salt of (trimethylsilyl)diazomethane with trimethylchlorosilane was reported to give bis(trimethylsilyl)diazomethane D. Seyferth, T. C. Flood, J. Organomet. Chem. 1971, 29, C25. 

Summary The reductive coupling of aminochlorosilanes and aminohydridochlorosilanes with lithium is discussed, first cross-coupling products with trimethylchlorosilane are presented. 

A quantitative fluorine-chlorine exchange occurs in the reaction of these lithium derivatives with trimethylchlorosilane trimethylfluorosilane and lithium chloride are formed. The resulting silahydrazone is isolated as the [2+2]-cycloaddition product [8]. 

Lil in boiling pyridine or other weak nucleophilic bases can cleave alkyl esters to alkyl iodides and lithium carboxylates (Scheme 28). The reaction is mainly used for mild, aprotic cleavage of esters to car-boxylates. The high degree of dissociation for Lil and the nucleophilic strength of the iodide ion explain the reaction with esters, which is not useful with the other halides. Trimethylchlorosilane and sodium iodide also give alkyl iodides from esters. ... 

The simplest example of such a system is depicted in Eq. (5.28). The lithium enolate of 2-(trimethylsilyl)cyclopropanone is formed by the reaction of [l-(tri-methylsilyl)vinyl]lithium with carbon monoxide (Eq. (5.29)). Treatment of the vi-nyllithium with CO, at atmospheric pressure, in THF at 15 C for 2 h followed by quenching with trimethylchlorosilane at -78 "C afforded a somewhat labile product, which decomposed during the usual hydrolytic work-up. Quenching with tert-butyldimethylchlorosilane/HMPA instead allowed isolation of the products. The major product was a silylated cyclopropane enolate. It is noteworthy that the overall sequence follows a formal [2-1-1 jcycloaddition (Eq. (5.28)). The silylated alle-nolate was also formed as a by-product as the result of a 1,2-anionic silicon rearrangement. 

P-Keto acids. A new synthesis of /i-keto acids involves the reaction of dianions of carboxylic acids with esters.6 The intermediates are trapped with trimethylchlorosilane and isolated as the trimethylsilyl esters. For example, isobutyric acid is converted into the dianion (1) by treatment with 2 eq. of lithium diisopropylamide in THF at 0°. Addition of I eq. of methyl pivalate (2) and an excess of trimethylchlorosilane yields the... 

ENOL ETHERS Trimethylchlorosilane. EPISULFIDES Sulfur monochloride. EPOXIDES Dimethylformamide dimethyl acetal. Dimethyloxosulfonium methylide. Iodine. Methylene bromide-Lithium. Methylphenyl-N-p-toluene-sulfonylsulfoximine. a -EPOXY SULFONES Hydrogen peroxide. 

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