Methyl silyl ketone

It is interesting to note that hydrolysis of iminosilacylcyclohexene 28 gave iminozirconium complex 27, while silazirconacyclohexenone 34 was converted into oxazirconacycle 36, which when treated with H20 gave the methyl silyl ketone 31 (Scheme 16). The differences between the reactivities of imi-nosilazirconacyclohexene 28 and silazirconacyclohexenone 34 would be due... 

The formation of ethers such as 1806 by EtsSiH 84b can also be catalyzed by trityl perchlorate to convert, e.g., benzaldehyde in 84% yield into dibenzyl ether 1817 [48]. The combination of methyl phenethyl ketone 1813 with O-silylated 3-phenyl-n-pro-panol 1818, in the presence of trityl perchlorate, leads to the mixed ether 1819 in 68% yield [48] (Scheme 12.15). Instead of trityl perchlorate, the combination of trityl chloride with MesSiH 84a or EtsSiH 84b and sodium tetrakis[3,5-bis-(trifluoro-methyl)phenyl]borane as catalyst reduces carbonyl groups to ethers or olefins [49]. Employing TMSOTf 20 as catalyst gives very high yields of ethers. Thus benzaldehyde reacts with O-silylated allyl alcohol or O-silylated cyclohexanol to give the... 

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. 

Dicarbonyl compounds.1 The reaction of enol silyl ethers with methyl vinyl ketone catalyzed by BF3 etherate results in 1,5-dicarbonyl compounds. Almost quantitative yields can be obtained, even from hindered ketones, by addition of an alcohol or even, to a less extent, of water. 

Michael addition.2 This triflate is an effective catalyst for Michael addition of enol silyl ethers to a,P-enones such as methyl vinyl ketone to provide adducts in 60-75% yield, equation (I). This variation is useful in Robinson annelations. 

Another 1,2-silyl migration from C to C was found during the reaction of an a-silyl cyclopropyllithium 42 with dichloromethyl methyl ether 43 to give the silyl ketone 44 (equation 36)87. 

Examples of the double hydroxylation reaction observed for several representative substrates illustrate the scope of this reaction (Table). Path a is generally preferred by the internal olefinic isomer of the enoi silyl ether of methyl alkyl ketones (entries 1-4, and 9) among which methyl sec-alkyl ketones (entries 1-3, and 9) overwhelmingly prefer the path a. Choice of the silyl group substantially affects path a vs. path b ratio path a becomes the favored pathway when the bulky tripropylsilyl group was used in place of the trimethylsilyl group (cf. entries 4 and 5). Thus steric hindrance at the site of the initial oxidation, the nature of the site of the proton removal (i.e., H in B), and the steric effect of the silyl group all contribute to the relative amounts of the two pathways. 

In a series of papers, Itoh and Mikami have reported the high yield, radical a-trifluoro-methylation of ketones using titanium euolates and Mefl/BEts as free radical generator and trifluoromethylating agent . The use of excess Ida and Ti(OPr-/)4 in the preparation of the titanium euolate represeuts the key to the success of the reaction (equation 41). Interest in this reaction stems from the fact that in general, the radical a-trifluoromethylation of ketones via lithium enolates is complicated by the easy defluorination of the a-CFs ketone by the parent enolate . For this reason, less reactive enolates such as silyl or germyl enolates have been initially used instead of lithium enolates" . 

This is a mild, simple and practical procedure for 1,4-addition of an aldehyde to methyl vinyl ketone, without converting the aldehyde into an enamine or a silyl enol ether. The products, substituted 5-ketoaldehydes, are important compounds, especially for the preparation of substituted 2-cyclohexen-1-one derivatives, which have been versatile starting materials for syntheses of natural products such as terpenoids. These 5-ketoaldehydes have been prepared previously by the 1,4-addition of modified aldehydes, i.e., morpholinoenamines of aldehydes,trimethylsilyl enol ethers of aldehydes in the presence of a Lewis acid, or diethylallylamine in the presence of a catalytic amount of a Ru complex, to methyl vinyl ketones. 

Dicarbonyl compounds are formed by reaction of silyl enol ethers with methyl vinyl ketones in the presence of BF3 Et20 and an alcohol (Eq. 84) [139]. 

Dibutyltin bis(triflate), Bu2Sn(OTf)2, is a mild Lewis acid which catalyzes clean Michael addition of enol silyl ethers [148]. The new catalyst enables use of various labile acceptors such as methyl vinyl ketone and 2-cyclopentenone which do not undergo smooth reaction with conventional Lewis acids. A variety of enol silyl ethers are also employable and thus 2-(trimethylsiloxy)propene, the simplest of this class of compounds, can be used. The adducts of enol silyl ethers of cycloalkanones with vinyl ketones are readily cyclized to give the desired annulated enones free of isomers. Consequently, a practical version of the Robinson annulation has been realized. 

Bis-silylation of methyl vinyl ketone with fluorinated disilane, FMe2SiSiMe2F, proceeds in the presence of phosphine-palladium catalyst to afford (Z)- 1,4-ad-dition product 67 in high yield (Eq. 33) [55]. 

A cheap and efficient method for synthesis of 2-triniethylsilyloxy-l,3-butadiene from methyl vinyl ketone was desired. The method had to be practical for molar scale preparations. Although a number of methods for the synthesis of silyl enol ethers from carbonyl compounds are known, none of them were applicable for this conversion. They were either too expensive for use on larger scale, or afforded poor yields on attempted synthesis. 

The fused salt CsOH-CsF acts as a desilylating reagent on ketene silyl acetals to give the equivalent enolate. The reaction proceeds at -60 °C. The equivalent reaction with methyl vinyl ketone proceeds by 1,4-addition (Scheme 2.32) [22]. 

---