1-Trimethylsilylvinyl ketones

The role of the trimethylsilyl group is to stabilize the enolate formed in the conjugate addition. The silyl group is then removed during the dehydration step. Methyl 1-trimethylsilylvinyl ketone can be used under aprotic conditions that are compatible with regiospecific methods for enolate generation. The direction of annulation of unsymmetrical ketones can therefore be controlled by the method of enolate formation. 

Another version of the Robinson annulation procedure involves the use of methyl 1-trimethylsilylvinyl ketone. The reaction follows the normal sequence of conjugate addition, aldol cyclization, and dehydration. 

TRIMETHYLSILYLOXY 1,3 BUTA DIENE, A REACTIVE DIENE, 58, 163 1-Trimethylsilylvinyl ketones, 58, 157, 162 1-Tnmethylsilylvinylmagnesium bromide, 58, 157... 

Among Michael acceptors that have been shown to react with ketone and ester enolates under kinetic conditions are methyl a-trimethylsilylvinyl ketone,295 methyl a-methylthioacrylate,296 methyl methylthiovinyl sulfoxide,297 and ethyl a-cyanoacrylate.298 Each of these acceptors benefits from a second anion-stabilizing substituent. The latter class of acceptors has been found to be capable of generating contiguous quaternary carbon centers. 

The stability of an a-silyl carbanion is responsible for the unproved synthetic utility of the Stork annulation over other annulations195,196. These reactions involve the Michael addition of an enolate ion to an enone, and in the absence of a a-silyl substituent suffer drawbacks due to the reversibility of the Michael reaction. However, the addition of enolate ions to a-trimethylsilylvinyl ketones is not reversible, owing to a-silicon stabilization of the canonical form 152 shown in equation 122. 

Methyl a-trimethylsilylvinyl ketone, 5,461-463. Recent synthesis from acrolein 1... 

Scheme 8). Conjugate addition of the resulting enamine-silyl ether to methyl a-trimethylsilylvinyl ketone in the presence of MgCl2 provided the cyclohex-enones. Using the prolinol-derived enamine, the annelated product was obtained with 77% ee.

ANNELATION f-Butyl-7-iodotiglate. l-Chloro-3-pentanone. 1-Fluorovinyl methyl ketone. 1-Lithiocyclopropyl phenyl sulfide. Methyl a-trimethylsilylvinyl ketone. 

Gallium(III) triflate catalysed the rearrangement of 2-substituted vinyl epoxides into /3,y-unsaturated carbonyl compounds with high regio- and chemo-selectivity with low catalyst loading. Alkyl-substituted trimethylsilylvinyl epoxides gave /i,y-unsaluralcd ketones, but aryl-substituted vinyl epoxides gave the aldehydes.80... 

Despite reports to the contrary early in 1980/ Danheiser and Carini have demonstrated that trimethylsilylallenes function as propargylic anion equivalents in reactions with ketones or aldehydes in the presence of titanium tetrachloride, regiospecifically forming homopropargylic alcohols. Unexpectedly, some silyl-allenes give mixtures of homopropargylic alcohols and trimethylsilylvinyl chlorides, but exposure of the crude reaction product to potassium fluoride in DMSO induces elimination from the latter to furnish exclusively the required alcohols ie.g. Scheme 113). 

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