Vinyl trimethylsilyl ether

Commercial polymers have been produced from methyl, ethyl, isopropyl, n-butyl, isotubtyl, t-butyl, stcaryl, benzyl and trimethylsilyl vinyl ethers. The polylmethyl vinyl ether) called PVM or Resyn is produced by the polymerization of the monomer by boron trifluoride in propane at —40°C in the presence of traces of an alkyl phenyl sulfide. The polymer may have isotactic, syndiotactic or stereoblock configurations depending on the solvent and catalyst used. 

With modified Aratani catalysts (2, R = Ph and A = CH2Ph), Reissig observed moderate enantioselectivities (30-40% ee for the trans cyclopropane isomer) for reactions between trimethylsilyl vinyl ethers and methyl diazoacetate [26], but vinyl ethers are the most reactive olefins towards cyclopropanation and also the least selective [30,31]. Other chiral Schiff bases have been examined for enantio-selection by using the in situ method for catalyst preparation that was pioneered by Brunner, but enantioselectivities were generally low [32]. 

Enantioselective Claisen rearrangement of allyl (a-trimethylsilyl)vinyl ethers in the presence of aluminium binaphthol derivatives gives ft-chiral y, <5-unsaturated acyl silanes with good ee (Scheme 33)114. 

Several examples of sequential isomerization/ring-closing metathesis for the preparation of heterocycles have also been performed by using two successive catalytic reactions catalyzed by two different ruthenium catalysts, but the second catalyst was introduced after completion of the first catalytic reaction. The isomerization was usually catalyzed by RuHCl(CO)(PPh3)3 [48], or RuCl2(= CHPh)(PCy3)(bis(mesityl)imidazolylidene) in the presence of trimethylsilyl vinyl ether [49], whereas a classical metathesis catalyst was subsequently introduced for the cyclization [48,49]. 

Notably, the asymmetric Claisen rearrangement of ci j-allylic ot-(trimethylsilyl)vinyl ethers with the chiral aluminum reagent produced optically active acylsilanes with the same absolute configuration as those from trans-allylic a-(trimethylsilyl)vinyl ethers (eq 5). ... 

Unfortunately, attempts to perform this substitution reaction on cyclohexenol and geraniol led to the exclusive formation of the corresponding silyl ethers. It thus would seem that one requirement for effective carbon-carbon bond formation is that allylic alcohols be secondary and have possess y,y-disubstitution. Pearson, however, discovered a method with less restriction on the natiue of the substrate he used allylic acetates with y-mono-substitution or primary alcohols [96]. Not only ketene silyl acetals but also a diverse set of nucleophiles including aUyl silane, indoles, MOM vinyl ether, trimethylsilyl azide, trimethylsilyl cyanide, and propargyl silane participate in the substitution of y-aryl allylic alcohol 90 to give allylated 91 (Sch. 45). Further experimental evidence suggests that these reactions proceed via ionization to allylic carboca-tions—alcohols 90 and 92 both afforded the identical product 93. 

Competitive addition of dichlorocarbene to various alkenes indicates that vinyl ethers are more reactive than I-alkenes.Hence, 2-alkoxy-l,l-dichlorocyclopropanes are usually prepared in good yield. The chloroform/base/phase-transfer catalyst method is the most often used. Substrates very sensitive to aqueous conditions, such as trimethylsilyl vinyl ethers will not, with a high degree of certainty, survive the phase-transfer catalysis conditions, thus other methods are used. ... 

Allylic l-(Trimethylsilyl)vinyl Ethers General Procedure138 ... 

A mixture of 10 mmol of allylic alcohol, 637 mg (2 mmol) of Hg(OAc)2 and 1.5 g (10 mmol) of ethyl l-(trimethylsilyl)vinyl ether is stirred at r.t. for 8- 12 h. The mixture is then poured into 5% aq KOH and extracted with hexane. After drying over Na2S04, the hexane extracts are concentrated. The crude residual is purified by column chromatography (hexane or Et20, hexane 1 50). 

A number of 2,3-dihydrobenzo[ ]furans can be made by the Ru-catalyzed olefin-metathesis approach in the presence of trimethylsilyl vinyl ether <04AG(E)4063>. The isovanillin derived benzofi ]furan was also made by the olefin metathesis approach <04H(63)I771>. 

When aldehydes or ketones enolize to enols under acidic conditions, the enols are not as stable as aldehydes or ketones. However, the formed enols can be fixed or protected by a trimethylsilyl group to form trimethylsilyl vinyl ethers, which then undergo the aldol reaction. This modification is known as Mukaiyama Aldol Reaction. 

Poly(vinyl alcohol) is very high in head-to-tail structures, based on NMR data. It shows the presence of only a small amount of adjacent hydroxyl groups. The polymer prepared from amorphous poly(vinyl acetate) is crystalline, because the relatively small size of the hydroxyl groups permits the chains to line-up into crystalline domains. Synthesis of isotactic poly(vinyl alcohol) was reported from isotactic poly(vinyl ethers) like poly(benzyl vinyl ether), TOly(f-butyl vinyl ether), poly(trimethylsilyl vinyl ether), and some divinyl compounds. ... 

The synthesis of dichloronorcarane from cyclohexene by the chloroform-base-PTC method has been improved further as has the preparation of a-halogeno-aP-unsaturated ketones via em-dihalogenocyclopropanes by employing trimethylsilyl vinyl ethers rather than ethyl vinyl ethers. The formation of gem-difluorocyclo-propanes proceeds in high yield (60— 90%) when chlorodifluoromethane is treated with halide ion and an epoxide in the presence of an olefin. The epoxide-halide ion combination is employed to produce a base of sufficient strength, and in sufficient concentration, to maximize the production of difluorocarbene oxiran and chloro-methyloxiran afford the most suitable bases when treated with chloride ion (Scheme 4). 

When 1,6-diene 46 was catalyzed by Grubbs carbene complex/trimethylsilyl vinyl ether or NiBr2(PPh3)2/Et2AlCl, exo-methylene cyclic compound 47 was obtained as the major product of the cycloisomerization (Scheme 27) (64,65). 

LPDE mediated allylic substitutions have been investigated widely. Substitution reaction of allylic alcohols with silyl ketene acetals, allyl silanes, indoles, methoxymethyl vinyl ether, trimethylsilyl azide, trimethylsilyl cyanide, and propar-gyl silanes proceeds with LPDE (Scheme 3.9) [32, 33]. An experiment with allylic alcohol (5,6) proved that these reaction proceeds via generation of allylic carbocation (Scheme 3.10). Also with a combination of LPDE and AcOH (1 mol%), more efficient allylic substitutions proceed (Scheme 3.11) [34]. 

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... 

Dienones, such as 4-[4-(trimethylsilyl)-2-butenyl]-3-vinyl-2-cyclohexenone, are useful precursors for these particular transformations the allylsilane side chain is too short for effective 1,4-addition, but just right for 1,6-addition, resulting in six-ring annulation. Three different Lewis acids can be used titanium(IV) chloride, boron trifluoride diethyl ether complex, and ethylaluminum dichloride. The best chemical yields and complete asymmetric inductions were obtained with ethylaluminum dichloride. 

To a solution of 310 mg (1.18 mmol) of 4-[(Z)-5-(trimethylsilyl)-3-pentenyl]-3-vinyl-2-cyclohcxcnone in 20 mL of toluene is added at —78, JC 0.75 mL (2.75 mmol) of a 50% solution of ethylaluminum dichloride in hexane. After stirring for 2 h at — 78 C. the mixture is quenched by addition of 20 mL of sat. aq NaHC Oj. After washing with 20 mL of brine the organic phase is extracted with three 30-mL portions of diethyl ether and dried over MgS04. The solvent is removed and the crude product is flash chromatographed (silica gel, EiOAc/petroleum ether 1 9) yield 114 mg (60%). 

Palladium-catalyzed bis-silylation of methyl vinyl ketone proceeds in a 1,4-fashion, leading to the formation of a silyl enol ether (Equation (47)).121 1,4-Bis-silylation of a wide variety of enones bearing /3-substituents has become possible by the use of unsymmetrical disilanes, such as 1,1-dichloro-l-phenyltrimethyldisilane and 1,1,1-trichloro-trimethyldisilane (Scheme 28).129 The trimethylsilyl enol ethers obtained by the 1,4-bis-silylation are treated with methyllithium, generating lithium enolates, which in turn are reacted with electrophiles. The a-substituted-/3-silyl ketones, thus obtained, are subjected to Tamao oxidation conditions, leading to the formation of /3-hydroxy ketones. This 1,4-bis-silylation reaction has been extended to the asymmetric synthesis of optically active /3-hydroxy ketones (Scheme 29).130 The key to the success of the asymmetric bis-silylation is to use BINAP as the chiral ligand on palladium. Enantiomeric excesses ranging from 74% to 92% have been attained in the 1,4-bis-silylation. 

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