Aryl trimethylsilyl ether

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°. ... 

I he reaction of aryl trimethylsilyl ethers catalyzed by (CH3),SiOTf with the D-ttlucosidc la (nnomeric mixture) results in the formation of essentially only the aryl -/ -Itlueosidc. ... 

Aryl and alkyl trimethylsilyl ethers can often be cleaved by refluxing in aqueous methanol, an advantage for acid- or base-sensitive substrates. The ethers are stable... 

Aryl and alkyl trimethylsilyl ethers can often be cleaved by refluxing in aqueous methanol, an advantage for acid- or base-sensitive substrates. The ethers are stable to Grignard and Wittig reactions and to reduction with lithium aluminum hydride at —15°. Aryl -butyldimethylsilyl ethers and other sterically more demanding silyl ethers require acid- or fluoride ion-catalyzed hydrolysis for removal. Increased steric bulk also improves their stability to a much harsher set of conditions. An excellent review of the selective deprotection of alkyl silyl ethers and aryl silyl ethers has been published. ... 

The combination Et3SiH/(C6F5)3B reduces acid chlorides to methyl groups (Eq. 138).281,282 If a smaller amount of triethylsilane is used, the same combination reduces aryl acid chlorides to the trimethylsilyl ethers of the benzyl alcohols.281,282... 

Diastereoselective syntheses of dihydrobenzo[f>]furans have been accomplished by a rhodium-catalyzed regioselective and enantiospecific intermolecular allylic etherification of o-iodophenols as a key step, providing the corresponding aryl ally ether 122, which leads to a dihydrobenzo[b]furan by treatment of the intermediate aryl iodide with tris(trimethylsilyl)silane and triethylborane at room temperature in the presence of air <00JA5012>. 

This methodology was applied to a two-step sequence for the preparation of enantio-merically enriched dihydrobenzo[h]furans (Scheme 10.11) [46]. Rhodium-catalyzed allylic etherification of (S)-47 (>99% ee), with the sodium anion of 2-iodo-6-methyl-phenol, furnished the corresponding aryl allyl ethers (S)-48/49 as a 28 1 mixture of regioisomers favoring (S)-48 (92% cee). Treatment of the aryl iodide (S)-48 with tris(trimethylsilyl)silane and triethylborane furnished the dihydrobenzo[h]furan derivatives 50a/50b as a 29 1 mixture of diastereomers [43]. 

Good yields are generally observed, especially for methyl ethers. The combination of boron tribromide with dimethyl sulfide has been found to be particularly effective for cleaving aryl methyl ethers.87 Trimethylsilyl iodide cleaves methyl ethers in a period of a few hours at room temperature.85 Benzyl and /-butyl systems are cleaved very rapidly, whereas secondary systems require longer times. The reaction presumably proceeds via an initially formed silyl oxonium ion ... 

Zirconium imido complexes have been used to carry out S 2 reactions of allylic chloride, bromide, iodide, and alkyl, aryl, and trimethylsilyl ethers in high yields at room temperature.12 The syn stereochemistry, an inverse secondary (k /k Oy = 0.88 obtained using the ( )-l-(r-butyldimethylsilyloxy)-3-deuterioprop-2-ene and the rate expression led the authors to suggest the reactions occurred via the mechanism in Scheme 4 with transition state (9). 

P-Aryl-ai,fi-unsaturated carbonyl compounds,2 In the presence of Pd(OAc)2-LiCl (1 5) aryl iodides react with allyl trimethylsilyl ethers in DMF to form (E)-/ -aryl-a,/ -unsaturated aldehydes and ketones. A similar reaction has been reported for allyl alcohols (7, 274). 

Reactions. Grignard reaction and hydrogenation of the appropriate methyl aryl ketone yielded isothymol.877 Carvacrol was formed in excellent (83%) yield on heating p-menth-l-ene oxide with Pd.878 Aromatic aldehydes can beprotected in situ by formation of a-aminoalkoxides and their O-trimethylsilyl ethers thus 4-formyl-benzoic acid could be protected and elaborated (Grignard reaction) into (264).879... 

Ether cleavage. The reagent is also useful for cleavage of aryl alkyl ethers to phenols (80-907o yield). It also cleaves dialkyl ethers to alkyl trimethylsilyl ethers which are then hydrolyzed to alcohols. This reaction is particularly useful for hydrolysis of methyl ethers (equation III). 

Demethylation of acid-sensitive aryl methyl ethers, such as 2,4-dimethoxyquinolines, can be accomplished using a trimethylsilyl iodide/DMAP reagent system, where DMAP is used as a Lewis base to prevent protonation of the alkene from the HIby-product. This reaction was utilized to form the quinoline-containing alkaloid natural product, atanine, from the Rutaceae family. 

Among the applications of allyl silanes reported this year their reaction with phenylselenyl chloride and subsequent oxidation of the resulting allyl selenides to allylic alcoholshas been used in the sequence outlined in Scheme IS. 3-Bromoallyltrimethylsilane therefore behaves as a hydroxypropenyl synthon. Nitroalkenes react with allylsilanes to give, after hydrolysis, y,S-unsaturated ketones, and a synthesis of substituted cyclopentenones based on this procedure has been described.Allyl trimethylsilyl ethers undergo a palladium-promoted coupling with aryl iodides to give /3-aryl-a,/3-unsaturated ketones, and palladium also catalyses the reaction of various aryl bromides with trimethylsilyl acetylene to produce ethynylated aromatics. 

Trimethylsilyl ethers are cleaved by C 6 l,4-Bi2C5F4 to give the aryl ether557 ... 

In the same context, the addition of 2-bromoketoesters to enals was developed by Rios et al. in the presence of TEA as a base in toluene at 4°C producing, upon catalysis with amine 8, the corresponding formal [2+1] cycloadducts in high yields of up to 95% and diastereoselectivities >92% de combined with enantioselectivities of up to 99% ee [135]. To make this type of reaction even more interesting from an environmental point of view, Vicario et al. have recently demonstrated that it was possible to react diethyl bromomalonate and enals in water at room temperature (rt) without using an external base [136]. The reaction, catalyzed by a chiral diarylprohnol trimethylsilyl ether, proceeded efficiently when (i-aryl-substituted a,P-unsaturated aldehydes were employed as substrates, while it failed when ahphatic enals were used. The corresponding formal cycloadducts were formed with enantioselectivities of up to >99% ee combined with good yields of up to 84%. In addition, amine 8 was apphed as catalyst to the enantioselective cyclopropana-tion of a-substituted a,P-unsaturated aldehydes with diethyl bromomalonate. 

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