Bis-Trimethylsilyl ether

Chiral 2-alky 1-1,3-propanediols.i Reaction of ( —)-menthone (1) with the bis(trimethylsilyl)ether 2 catalyzed by trimethylsilyl triflate gives the more stable equatorial isomer (3) of a spiroketal. Ring cleavage of the equatorial bond of the... 

Acetalization of ketones was also effected using Noyori s kinetic acetalization protocol. Thus, bis-trimethylsilyl-ethers readily react with cyclohexanones to give 1,3-dioxanes in good yield (Equation 73) <1997J(P1)2789>. 

The radical reductive cyclisation of diesters to acyloins (see also Section 5.9.1, p. 628) is an important method of synthesis for ring sizes from four-membered upwards. The example selected here is 2-hydroxy-3-methylcyclopent-2-enone ( corylone ) (29) (Expt 7.10), which is an important perfumery and flavouring material.53 In the first step (i), methyl acrylate is converted into its dimer with tris(cyclohexyl)phosphine in pyridine solution.5b Step (ii) is the protection of the double bond by conversion into the dimethylamino adduct. The acyloin reaction is step (iii), and the product is trapped as its bis(trimethylsilyl)ether. Finally, in step (iv), the protecting dimethylamino and trimethylsilyl groups are removed by passage down a column of silica gel. 

S)-l-Alkyl-l,2, 4-tetrahydroisoquinolines. The bis(trimethylsilyl) ether (2) of 1 has been used as a chiral auxiliary to effect alkylation of tetrahydroisoquinoline (equation 1) with high enantioselectivity. The chiral propanediol is much more effective than (R)-(— )-a-phenethylamine, and moreover leads consistently to (S)-l-alkyl derivatives. 

Cyclobutanediones, once exotic compounds represented by a few perhalo derivatives, have become readily available as a result of new synthetic developments in recent years. These include the modified acyloin condensation 52) in which the intermediate enediolate is trapped as bis-trimethylsilyl ether (28) which can be converted to cyclobutanedione by reaction with bromine or hydrolyzed to acyloin and oxidized in a separate step. In addition to this efficient and general method, bi- or polycyclic unsaturated cyclobutanediones (30) have become available from photolysis of bridged cyclohexenediones (29) to be discussed in the following section. Photocycloaddition of dichlorovinylene carbonate (DCVC) to olefins53) promises to provide a third route if the problems associated with hydrolysis of the photoadducts (31) can be overcome. 

Estradiol bis(trimethylsilyl) ether (235 Scheme 50) has been converted into a diasteromeric mixture of adducts (236) which were hydrolyzed by aqueous acetic acid to a mixture of the isomeric enones (237 36% yield) and (238 9% yield).This provides an especially direct route for the introduction of functionality at C-1, which would otherwise require a multistep sequence. Reductive silylation has also been used to convert anisole into enone (239)which, following a kinetic resolution, has been used in an en-antioselective synthesis of (-i-)-a-curcumene (240 Scheme 51). The silyl substituent was employed to control the stereochemical and regiochemical aspects of subsequent steps. 

The bis(trimethylsilyl) ether of hydroquinone is oxidized by pyridinium chlorochromate to -benzoquinone (equation 342) [610]. 

Fluoride-induced fragmentation reactions were used in two stages of a synthesis of hexahydrocannabi-nol methyl ether (144 Scheme 52). One of the phenolic hydroxy functions in the resorcinol derivative (140) was selectively liberated from the SEM ether to give the diol (141), which was converted to the bis (trimethylsilyl) ether (142). Subsequent treatment with CsF resulted in a 1,4-elimination to the o-quinone methide (143) intermediate, which underwent an intramolecular [4 -i- 2] cycloaddition to give the product in good yield. 

Acyloin condensation of 2,2-dimethylmalonate with sodium in liquid ammonia using chloro-trimethylsilane gave the c 5-l,2-bis(trimethylsilyl) ether 5. ... 

Silyl enol ethers, known as chemically stable and easy handled enolates, can be protonated by a strong Bronsted acid. Our group demonstrated that a Lewis acid-assisted Bronsted acid (LBA 17), generated from optically pure binaphthol and tin tetrachloride, was a chiral proton source of choice for asymmetric protonation of silyl enol ethers possessing an aromatic group at the a-position [33, 34]. Binaphthol itself is not a strong Bronsted acid, however, LBA 17 can proto-nate less reactive silyl enol ethers since the acidity of the phenolic protons of 17 is enhanced by complexation with tin tetrachloride. The catalytic asymmetric protonation of silyl enol ethers was accomplished for the first time by LBA 18. Treatment of ketene bis(trimethylsilyl)acetal 60 with 0.08 equiv of LBA 18 and a stoichiometric amount of 2,6-dimethylphenol as an achiral proton source afforded (S)-2-phenylpropanoic acid (61) with 94% ee (Scheme 10) [35]. LBA 19 derived from binaphthol monoisopropyl ether has been successfully applied to the enantioselective protonation of meso 1,2-enediol bis(trimethylsilyl) ethers under stoichiometric conditions [36]. 

Derivate des intermediaren Bis-Enols erhalt man bei der Isomerisierung der entsprechen-den Diacetate108 oder Bis-[trimethylsilyl]-ether (Silyloxy-Cope-Umlagerung109). 

The bis-trimethylsilyl ethers of stereoisomeric 5,7-undecanediol 78 (as well as the free diols) give upon chemical ionization (protonation with QH9) MH+ ions, which show two major processes (reaction 41). One corresponds to a Grob-type fragmentation 05-cleavage) of the ion 79 (formed by loss of Me3SiOH from protonated 78) to yield the silylated aldehyde 80. The second major reaction path involves loss of CH4 from MH+, followed by cyclization of the intermediate 81 (siloxy transfer) to 82 and ft-cleavage (loss of 1-hexene) to generate 8467. This reaction sequence, in which a centrally located structural unit rather than a peripheral one is eliminated, is rarely observed under chemical ionization and deserves further study. 

A closely related methodology (route c) involves the dianion from a diketone (R = Me) with the anion of dimethyl malonate (R = Me) (ref.25). The bis-trimethylsilyl ether from methyl acetoacetate has been interacted with the ketalised acid chloride shown (R = CgH ) to furnish the methoxy carbonyl derivative of olivetol (route d) (ref.26). It was also found that pentane-2,4-dione with dimethyl malonate in the presence of sodium hydride afforded methyl orsellinate (ref.26). In a biomimetic approach (route e) a tetraketone has been enzymically cyclised to give the corresponding orsellinic acid (R=H, R = alkyl) (ref. 27). 

Other routes to the parent orsellinic acid have been listed (ref. 119). Cycloaromatisation reactions have been employed for the synthesis of 2-hydroxy-6-methylbenzoic acid and for the 4-methyl isomer as shown in the scheme The syntheses which are claimed to be regiospecific involve two different pathways in the reaction of 4-methoxybut-3-en-2-one with the bis-trimethylsilyl ether of 1-methoxybuta-1,3-diene, dependent on the conditions used (ref. 120). 

The bis(trimethylsilyl) ether (36) with fluorophosphoranes gave the monocyclic phosphoranes (37), except with tetrafluorophosphoranes and... 

The most widely used compound is known as hexamethyl-disiloxane (HMDS), bis (trimethylsilyl) ether, or bis (trimethylsilyl) oxide. Figure 1. ... 

Synthesis of Primary Amines. The nucleophilic properties of this reagent may be utilized in the Sn2 displacement of primary alkyl bromides, iodides, and tosylates to form bis(trimethylsilyl) amines (1) (eq 8). HCl hydrolysis of (1) allows isolation of the corresponding hydrochloride salt of the amine, which may be readily separated from the byproduct, bis(trimethylsilyl) ether. In one example a secondary allylic bromide also underwent the conversion with good yield. 

Silcorel BNS2FX [Reliance Silicones http //www. reiiancesiiicones. com] Hexamethyidisiloxane CAS 107-46-0 EINECS/ELINCS 203-492-7 Synonyms Bis (trimethylsilyl) ether Bis (trimethylsilyl) oxide Disiloxane, hexamethyl- HMDSO Oxybis (trimethylsilane)... 

Pyrolysis of the bis-trimethylsilyl ether (652) also proceeds by cyclobutene ring-opening followed by internal [4 4- 2] cycloaddition. This is very different from the thermal transformation of (653) into (654), illustrating the care which must be taken in generalizing about the behaviour of a system when the substituents are varied. ... 

The highly stable product, bis(trimethylsilyl) ether or hexamethyldisiloxane, is produced in many reactions involving trimethylsilyl groups and is often discarded. Its inertness, however, makes for several uses, including liquid bandages such as Cavilon spray, which can be sprayed on broken or tender skin as protection against infection. 

Retention times given relative to the bis(trimethylsilyl) ether of methyl deoxycholate. 

The Lewis acid-catalysed acetaladons of alkyl D-gluco- and D-galactopyranoside-4,6-diols and their 4,6-bis(trimethylsilyl) ethers with methyl 2,2-(diphenylthio)propanoate or methyl pyruvate, respectively, have been studied in detail. It was observed that these reactions are often accompanied by anomerization and by isomerization of the initial, kinetic acetal to the thermodynamically stable diastereomer with an axial COjMe group. An example is given in Scheme 2. The 4,6-0-methyl pyruvate-based acetal 14 has been synthesized from benzyl a-D-mannopyranoside via the 4,6-0-(1,1,3,3-tetraisopropyldisUoxane-l,3-diyl)-piotected derivative 13 this procedure requires fewer protection/deprotection steps than use of the more common 4,6-bis(trimethylsilyl) ether as intermediate. ... 

Alternate Names bis(trimethylsilyl) ether bis(trimethylsilyl) oxide. 

Schwarz, H. Koppel, C. B( ilmarm, F. Electron Impact-Induced Fragmentation of Acetyl ie Conq>ounds. XII. Rear-rangem t of Bis(Trimethylsilyl) Ethers of Unsatnrated a,ra-Diols and Mass Spectrometric Identification of Isomeric Phenols. Tetrahedron 1974,30, 689-693. 

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