Trimethylchlorosilane silylation with

Whereas silylations with trimethylchlorosilane (TCS) 14 (b.p. 57 °C) demand the presence of a base to neutralize the HCl evolved, giving rise to the hydrochloride of the base, the use of hexamethyldisilazane (HMDS) 2 (b.p. 126 °C), in particular in the presence of 0.01-0.05 equivalents of acidic catalysts such as TCS 14 or ammonium sulfate, should normally be preferred as the preparative silylating reagent, because HMDS 2 ... 

Last but not least HMDS 2 is, in the laboratory and in pilot plants, quite stable when stored in a normal closed vessel whereas trimethylchlorosilane (TCS) 14 should be stored in a hood, because it reacts with humidity to hexamethyldisilox-ane 7 and HCl. Because HMDS 2 is a very non-polar compound, the silylation of very polar compounds, e.g. purines or pteridines, with HMDS 2 wiU often proceed only on addition of a polar solvent such as pyridine which is, however, readily removed after silylation, with excess HMDS 2, on codistillation with abs. xylene. Interestingly, it was recently reported that addition of catalytic amounts of iodine dramatically accelerates the silylation of alcohols, in particular tertiary alcohols, with HMDS 2 in CH2CI2 at room temperature [63]. 

Mesoporous silicas with various pore sizes are hydrophobic by silylation with silanes. Changes in the pore structure as a result of the silylation reactions are monitored in order to assess the distribution of the hydrophobic groups. Extensive polymerization of dimethyldi-chlorosilane causes blocking of the micropore fraction. For silica with pore sizes in the supermicroporous range (2nm), this leads to hydrophobization of almost exclusively the outer surface. While for trimethylchlorosilane a smaller number of molecules react with the surface, modification is more homogeneous and an open structure is optimally preserved. Both silanes lead to lower surface polarity and increased hydrothermal stability, i.e., preservation of the porous structure during exposure to water.12231... 

Silyl enamines have been prepared from cyanohydrins RR QOSiMcaiCN by reductive silylation with McaSiCl/Li. Photodesilylation by HCl gas in dry diethyl ether or by trimethylchlorosilane in methanol gave, after neutralization, the enamines, RR C=C(NH2)SiMc3 which were surprisingly stable. 

Very stable silyl ethers form when cellulose is treated with trimethylchlorosilane or with bis(trimethylsily l)acetamide... 

Wouters, B.H., Chen, T., Dewilde, M., and Grobet, PJ. 2001. Reactivity of the surface hydroxyl groups of MCM-41 towards silylation with trimethylchlorosilane. Micropor. Mesopor. Mater. 44-45 453 57. 

Vinyl halides, such as cis- and trans- i-iodo-3-hexene [33], undergo a one-electron reduction with expulsion of a hahde ion to give a vinyl radical that is further reduced and protonated. When vinyl halides are electrolyzed in the presence of trimethylchlorosilane, silylated products are obtained [34]. 

Zhao XS, Lu GQ (1998) Modification of MCM-41 by surface silylation with trimethylchlorosilane and adsorption study. J Phys Chem B 102 1556-1561... 

One of the better processes for the conversion of adenine to adenosine involves the initial conversion of adenine to the corresponding N -benzoyl derivative with benzoyl chloride in pyridine. Then, as shown in Scheme 12.100, silylation with trimethylchlorosilane in hexamethyldisilazane [(CH3)3Si]2NH solvent at reflux yielded a silyl derivative that was heated in 1,2-dichloroethane (CICH2CH2CI) at reflux with trimethylsilyl perchlorate [(0113)3810104] and l-0-acetyl-23,5-tri-0-benzoyl-P-D-ribofuranose for 12 h. The resulting crude, protected adenosine was converted to unprotected material by standing at room temperature with methano-lic ammonia followed by recrystaflization from aqueous methanol. 

The distillate was dissolved in a mixture of 350 ml of dry diethyl ether and 45 g of dry triethylamine (dried over powdered KQH). Trimethylchlorosilane (45 g) was added in 20 min with cooling at about 10°C. After standing for 1 h at room temperature the precipitate was sucked off on a dry sintered-glass funnel and rinsed with pentane. The filtrate was concentrated in a water-pump vacuum- The small amount of salt which precipitated during this operation was removed by a second suction filtration. Subsequent distillation afforded the trimethyl silyl ether, b.p. 100°C/15 mmHg, 1.4330, in 944 yield. 

Trimethylsilyl iodide [16029-98-4] (TMSI) is an effective reagent for cleaving esters and ethers. The reaction of hexamethyldisilane [1450-14-2] with iodine gives quantitative conversion to TMSI. A simple mixture of trimethylchlorosilane and sodium iodide can be used in a similar way to cleave esters and ethers (8), giving silylated acids or alcohols that can be Hberated by reaction with water. 

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). 

Carboxylic acids such as acetic acid react with alcohols such as methanol or with methoxytrimethylsilane 13 a in the presence of trimethylchlorosilane (TCS) 14 in THF or 2-methyl-THF to give esters such as methyl acetate in 97% yield and hex-amethyldisiloxane 7. Even methyl pivalate can be readily prepared in 91% yield [111]. Reaction of a variety of carboxylic acids, for example N-benzoylglycine 329, with two equivalents of yS-trimethylsilylethanol 330 and with 14 has been shown to afford esters such as 331 in 98% yield [112, 112 a]. Likewise, silylated carboxylic acids react with silylated alcohols or thiophenols in the presence of 4-trifluoro-methylbenzoic anhydride and TiCl4/AgCl04 to furnish esters or thioesters in high yields [113, 114] (Scheme 4.43). 

The many derivatizing reagents commercially available include methanolic HC1 and diazomethane for methylation, and iV,(9-bis(trimethylsilyl)trifluoroacetamide (BSTFA), with or without 1% trimethylchlorosilane (TMCS), for silylation. Using BSTFA, hydroxyl moieties also can be silylated, giving the corresponding trimethylsilyl ethers. 

Elimination of trimethylchlorosilane and nitrogen occurs when the (phos-phino)(silyl)diazomethane la is reacted with para-toluenesulfinyl chloride at low temperature. The formation of the four-membered heterocycle 92, obtained in 87% yield, can be rationalized by a multiple-step mechanism involving the formation of the (phosphino)(sulfinyl)carbene 2v. The insertion of the (phosphoryl)(sulfenyl)carbene 91, resulting from a 1,3-oxygen shift from sulfur to phosphorus in 2v, into a carbon-hydrogen bond of a diisopropylamino group readily accounts for the formation of 92.84... 

A 30-mL flask containing 0.2 mL of TTX solution (250 MU) and 0.5 mL of 1.5 N NaOH is heated at 80-90 °C for 30 min to derive C -base from TTX (18, 25). After being cooled to room temperature, the reaction mixture is adjusted to pH 3-5 with 10% HCl and extracted 3 times with 2 mL of n-butanol. The combined extracts are evaporated to dryness under reduced pressure. The C -base in the residue is converted to the trimethylsilyl derivative in the presence of N,0-bis(trimethyl-silyl)acetamide, trimethylchlorosilane and pyridine (2 1 1). This derivative is then applied to GC-MS (Hitachi 063 gas chromatograph column (2 m x 3 mm I.D.), Chromosorb W coated with 3% OV-1, temperature 180-250 °C (5 °C/min) Hitachi RMU 6 MG mass spectrometer ionization voltage 70 eV, carrier gas helium). 

Gas chromatographic separation of amphenicols is further complicated by the need for derivatization of their polar functional groups. Silyl derivatives formed by treating sample extracts with N,O-bis(trimethylsilyl)acetamide (49), trimethylsilyl N,N-dimethyl carbamate (47), N,O-bis(trimethylsilyl)tri-fluoroacetamide/trimethylchlorosilane (99 1) mixture (32, 51), or mixture of... 

Some researchers have tried to stabilize the MCM wall by a complete hydrofobization of the surface, replacing every silanol group with a trimethy Isi ly 1 group, using e.g. trimethylchlorosilane of hexamethyldisilazane [9], Although this treatment is very effective in se, it yields a surface that is completely unreactive towards subsequent grafting of transition metals. We therefore present a silylation procedure with dimethyldichlorosilane (DMDCS), which allows - upon hydrolysis - a recreation of surface silanols. 

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. 

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... 

Deprotonation-silylation of hydrazones with n-butyllithium in THF as the base followed by quenching with trimethylchlorosilane has been reported to afford the desired SMA derivative in good yield.154,155... 

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