TMS ether

NCSBu2Sn)20 1%, THF, H20. Acetonides and TMS ethers are also cleaved under these conditions, but TBDMS, MTM, and MOM groups are stable. This catalyst has also been used to effect transesterifications. ... 

Trimethylsilyl ethers are quite susceptible to acid hydrolysis, but acid stability is quite dependent on the local steric environment. For example, the 17o -TMS ether of a steroid is quite difficult to hydrolyze. 

The triethylsilyl ether is approximately 10-100 times more stable than the TMS ether and thus shows a greater stability to many reagents. Although TMS ethers can be cleaved in the presence of TES ethers, steric factors will play an important role in determining selectivity. The TES ether can be cleaved in the presence of a /-butyldimethylsilyl ether using 2% HE in acetonitrile. In general, methods used to cleave the TBDMS ether are effective for cleavage of the TES ether. 

Trimethylsilyl ethers are readily cleaved by fluoride ion, mild acids, and bases. If the TMS derivative is somewhat hindered, it also becomes less susceptible to cleavage. A phenolic TMS ether can be cleaved in the presence of an alkyl TMS ether [Dowex lX8(IfO ), EtOH, rt, 6 h, 78% yield]. ... 

From a TMS ether PhCHO, TESH, TMSOTf, 96% yield. This method is effective for the preparation of allyl ethers (85% yield). 

Direct oxidative cleavage of the TMS ether is possible with... 

AI2O3, H2O, hexanes, 81-98% yield. These conditions are selective for the primary derivative. TBDPS and TMS ethers are also cleaved. The use of alumina in a microwave oven is also effective (68-93% yield). ... 

Like most other ethers, which we ll study in the next chapter, TMS ethers are relatively unreactive. They have no acidic hydrogens and don t react with... 

TMS ethers can be removed by treatment with fluoride ion as well as by acid-catalyzed hydrolysis. Propose a mechanism for the reaction of cyclohexyl TMS ether with LiF. Fluorotrimethylsilane is a product. 

Horvath, K. and Molnar-Perl, I. (1997). Simultaneous quantitation of mono-, di- and trisaccharides by GC-MS of their TMS ether oxime derivatives II. In honey. Chromatographia 45,328-335. 

BSTFA or BSA Reagents of choice for the formation of N-TMS derivatives. May promote the formation of enol-TMS ethers unless ketone groups are protected. 

The mass spectra of TMS ethers are characterized by weak or absent molecular ions the [M-15] ion formed by cleavage of a methyl to silicon bond is generally more abundant. This ion can be used to determine the molecular weight provided that it is not mistaken for the molecular ion itself. Dissociation of the molecular ion often results in prominent secondary fragment ions containing the ionized dimethylsiloxy group attached to a hydrocarbon portion of the molecule. In common with alkyl ethers,... 

The electron ionization (El) mass spectra of TMS ethers and esters are generally characterised by weak or absent molecular ions. The [M—15]+ ion formed by loss of a methyl radical is generally abundant and in the case of alcoholic functions, the loss of a trimethylsilanol molecule [M—90]+ is also diagnostic. The peak at mJz 73, corresponding to the TMS group, is important in nearly all the TMS-derivative mass spectra. Figure 8.2 shows the fragmentation of TMS esters and ethers in mass spectrometric analyses. 

More recently on-line pyrolysis with HMDS has been performed successfully even if the pyrolysis interface was kept at 250°C. In fact, Domenech-Carbo and colleagues [57,58] have obtained very good results on a variety of art materials and on real paint samples as well. They have applied Py-GC/MS with on-line trimethylsilylation to the characterization of diterpenoid resins and, in contrast to previous literature data, the derivatization method enabled not only the identification of resinous carboxylic acids in the form of TMS esters, but also an efficient conversion of hydroxyl groups to TMS ethers. 

The trimethylsilyloxy (TMSO) group is stable under the coupling conditions in acetonitrile (Table 12, number 6). After oxidative dimerization the TMS-ether can be mildly hydrolyzed (H+ and H2O) to the phenol or converted to a dibenzofuran. 1,2-Dialkoxybenzenes have been trimerized to triphenylenes (Table 5, numbers 7, 8). The reaction product is the triphenylene radical cation, which is reduced to the final product either by zinc powder or in a flow cell consisting of a porous anode and cathode [188]. Anodic trimerization of catechol ketals yields triphenylene ketals, which can function as a platform for receptors, for example, in an artificial caffeine receptor [190]. 

Scheme 21 Cathodic cyclization of unsaturated esters yield (alcohol) 60%, yield (TMS ether) 67%.

Endogenous and exogenous androgens can be derivatized with trimethylsilyl (TMS) for hydroxy functions and by 0-methylation for ketones, and analyzed with GC-FID or GC-MS (Shimada et al., 2001). MS is more prevalent due to unequivocal identification and greatly increased sensitivity but FID is still used in laboratories for some steroids. Sterols have typically been analyzed by GC-FID and GC-MS with derivatization to optimize peak shape (Shimada et al., 2001), and bile acids can be derivatized with M-butyl ester-TMS ether and analyzed by GC-FID from plasma samples (Batta et al., 1998). Juricskay and Telegdy (2000) reported an assay capable of analyzing 28 steroids in urine samples using GC-FID. 

Fig. 6. GC-MS key ion fragmentograms of ot/z 215 and associated mass spectra (a) the stanol elution range for a feedlot dust extract, (b) the same range for the silylated extract, (c) ey i-5 3-stigmastanol, and (d) i i-5 3-stigmastanol-TMS ether. C, are the carbon skeletons of the other isomers.

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