Cleavage of trimethylsilyl ethers

Cleavage of trimethylsilyl ethers to the parent alcohols occurs quite readily on exposure to nucleophiles such as methanol, especially in the presence of... 

MeO /MeOH cleavage of trimethylsilyl ethers occurs much more rapidly (by a factor of approximately 104) than the corresponding cleavage of tert-butyldimethylsilyl ethers. Both types of ether, however, are very rapidly cleaved by F. ... 

The oxidative cleavage of carbon-carbon bonds in vicinal diols [756, 759] is a reaction widely used in saccharide chemistry. Besides its application in this reaction, periodic acid achieves the oxidative coupling [757] or oxidation to quinones [758] of polynuclear aromatic hydrocarbons, the oxidation of methyl groups in aromatic compounds to carbonyl groups [760], the conversion of epoxides into dicarbonyl compounds [761], and the oxidative cleavage of trimethylsilyl ethers of acyloins to carboxylic acids [755]. 

Because of the high stability of the triphenylmethyl carbocation, the reductive ether cleavage of trityl ethers with EtySiH/trimethylsilyl triflate (TMSOTf) is highly successful. This reaction even occurs in the presence of highly reactive sugar ketals, leaving the ketals intact (Eq. 126).269... 

Cleavage of SEM ethers. (Trimethylsilyl)ethoxymethyl (SEM) ethers are cleaved by Bu4NF in combination with HMPT and 4-A molecular sieves in 1 hour at 100° in 90-98% yield. The reaction requires 15 hours in the absence of the... 

As with preparing allyl of benzyl halides and alkali useful route to benzylalkali R-R coupling. Benzylalkali prepared by (1) addition of arylalkenes, (2) cleavage of benzyl ethers (equation 28), (3) transmetallation (equations 29-31), and (4) metallation of methyl substituted aromatics. a, a -Bis(trimethylsilyl)benzyl potassium can be prepared by metallation with a mixture of butyllithium and potassium 3-methyl-3-pentanolate in THF. ... 

Similar to the deprotonation of enol radical cations, silyl enol ether radical cations can undergo loss of trialkylsilyl cations (most likely not as ionic silicenium ions [190]). Based on photoinduced electron transfer (PET), Gass-man devised a strategy for the selective deprotection of trimethylsilyl enol ethers in the presence of trimethylsilyl ethers [191]. Using 1-cyanonapthalene (1-CN) ( = 1.84 V) in acetonitrile/methanol or acetonitrile/water trimethylsilyl enol ether 93 ( j = 1.29 V) readily afforded cyclohexanone 64 in 60%. Mechanistically it was proposed that the silyl enol ether radical cation 93 undergoes O-Si bond cleavage, most likely induced by added methanol [192-194], and that radical 66 abstracts a hydrogen from methanol. Alternatively, back electron transfer from 1-CN - to 66 would yield the enolate of cyclohexanone which should be readily protonated by the solvent. 

Alkylation of fl-aryleyclopentanones. Addition of 10 mole% of CuCN to the lithium enolate prepared from /3-arylcyclopentanones and LDA increases the amount of the less stable product of alkylation. Polyalkylation is also suppressed. Similar results are obtained when methyl- or phenylcopper is added to the enolate prepared by alkyUithium cleavage of trimethylsilyl enol ethers. The mechanism by which Cu(I) influences these alkylations is not as yet understood. The regiospecificity of enolate formation in the example Illustrated in equation (I) has been attributed to a directing efiect of the proximate phenyl group. This effect is also observed in the deprotonation of -arylcyclohexanones. Quantitative, but not qualitative, differences exist between five- and six-membered rings, probably because of conformational differences. ... 

Cleavage of TBS ethers. Trimethylsilyl ethers are cleaved on exposure to Zn(Bp4)2 in water. ... 

Deprotection of trimethylsilyl ether has also been accomplished (88-100%) on KIO clay [47] or oxidative cleavage (70-95%) in the presence of clay and iron(III) nitrate [48]. Another oxidative deprotection of trimethylsilyl ethers using supported potassium ferrate, K2pe04 and MW has been reported [49]. 

Lithium triethylborohydride reducing agent, mild nucleoside chemistry Tris (trimethylsilyl) silane reducing agent, mild reductive cleavage of cyclic ethers... 

Scheme 3.2 Mechanism of non-hydrolytic cleavage of the ether C-O bond by trimethylsilyl iodide...

Silvl Ethers.- The reductive cleavage of silyl ethers employing NaH in HMPA or DMPU has been reported. Methyl 6-Q-tert-butyldimethylsilyl-a-D-glucopyranoside and the 4,6-di-Q-tert-butyldimethylsilyl ether of D-glucal were each deprotected in 90% yield under these conditions. The deprotonation of a silyl ether with base is mentioned in Chapter 13. The trimethylsilyl ethers of a number of D-glucose derivatives have been prepared and characterized by H-, c- and Si-n.m.r. spectroscopy and mass spectroscopy. 

JUNG OLAH - VORONKOV Etherdeavage Cleavage of ethers or esters, carbamates, phosphorates with trimethylsilyl Iodides. Oeoxygenation of sulfoxides. 

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]. ... 

Trichloroacetic acid, pKa of. 759 Trifluoroacetic acid, pKa of, 756 Trifluoromethylbenzene, electrostatic potential map of, 565 Triglyceride, see Triacylglycerol, 1061 Trimethylamine, bond angles in, 919 bond lengths in, 919 electrostatic potential map of, 921 molecular model of, 919 Trimethylammonium chloride, IR spectrum of, 953 Trimethylsilyl ether, cleavage of, 627-628... 

The synthetic problem is now reduced to cyclopentanone 16. This substance possesses two stereocenters, one of which is quaternary, and its constitution permits a productive retrosynthetic maneuver. Retrosynthetic disassembly of 16 by cleavage of the indicated bond furnishes compounds 17 and 18 as potential precursors. In the synthetic direction, a diastereoselective alkylation of the thermodynamic (more substituted) enolate derived from 18 with alkyl iodide 17 could afford intermediate 16. While trimethylsilyl enol ether 18 could arise through silylation of the enolate oxygen produced by a Michael addition of a divinyl cuprate reagent to 2-methylcyclopentenone (19), iodide 17 can be traced to the simple and readily available building blocks 7 and 20. The application of this basic plan to a synthesis of racemic estrone [( >1] is described below. 

An important stage in the synthesis has been reached. It was anticipated that cleavage of the trimethylsilyl enol ether in 18 using the procedure of Binkley and Heathcock18 would regiospecifically furnish the thermodynamic (more substituted) cyclopentanone enolate, a nucleophilic species that could then be alkylated with iodo-diyne 17. To secure what is to become the trans CD ring junction of the steroid nucleus, the diastereoisomer in which the vinyl and methyl substituents have a cis relationship must be formed. In the... 

Alkyl esters are efficiently dealkylated to trimethylsilyl esters with high concentrations of iodotrimethylsilane either in chloroform or sulfolane solutions at 25-80° or without solvent at 100-110°.Hydrolysis of the trimethylsilyl esters serves to release the carboxylic acid. Amines may be recovered from O-methyl, O-ethyl, and O-benzyl carbamates after reaction with iodotrimethylsilane in chloroform or sulfolane at 50—60° and subsequent methanolysis. The conversion of dimethyl, diethyl, and ethylene acetals and ketals to the parent aldehydes and ketones under aprotic conditions has been accomplished with this reagent. The reactions of alcohols (or the corresponding trimethylsilyl ethers) and aldehydes with iodotrimethylsilane give alkyl iodides and a-iodosilyl ethers,respectively. lodomethyl methyl ether is obtained from cleavage of dimethoxymethane with iodotrimethylsilane. 

This procedure illustrates a new three-step reaction sequence for the one-carbon ring expansion of cyclic ketones to the homologous tt,/3-unsaturated ketones. The key step in the sequence is the iron(III) chloride-induced cleavage of the central bond of trimethyl-silyloxycyclopropanes which me obtained by cyclopropanation of trimethylsilyl enol ethers. The procedure for the preparation of 1-trimethylsilyloxycyclohexene from cyclohexanone described in Part A is that of House, Czuba, Gall, and Olmstead. ... 

The use of iodotrimethylsilane for this purpose provides an effective alternative to known methods. Thus the reaction of primary and secondary methyl ethers with iodotrimethylsilane in chloroform or acetonitrile at 25—60° for 2—64 hours affords the corresponding trimethylsilyl ethers in high yield. The alcohols may be liberated from the trimethylsilyl ethers by methanolysis. The mechanism of the ether cleavage is presumed to involve initial formation of a trimethylsilyl oxonium ion which is converted to the silyl ether by nucleophilic attack of iodide at the methyl group. tert-Butyl, trityl, and benzyl ethers of primary and secondary alcohols are rapidly converted to trimethylsilyl ethers by the action of iodotrimethylsilane, probably via heterolysis of silyl oxonium ion intermediates. The cleavage of aryl methyl ethers to aryl trimethylsilyl ethers may also be effected more slowly by reaction with iodotrimethylsilane at 25—50° in chloroform or sulfolane for 12-125 hours, with iodotrimethylsilane at 100—110° in the absence of solvent, " and with iodotrimethylsilane generated in situ from iodine and trimcthylphenylsilane at 100°. ... 

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