Phenylthiomethylstannylation of silyl enol ethers and silyl dienol ethers

Silyl enol ethers (2) react with tributyl [(phenylthio) chloromethyl] stannane (1) in the presence of Zinc bromide to give β-phenylthiomethylstannyl ketones (3) in good yields. Silyl dienol ethers (4) mainly give products (5) due to γ-attack, under these conditions.     

Alkylation of silyl enol ethers with pummerer generated vinyl thionium ions

Si]yl enol ethers (1,2) are γ-alkylated in moderate yields by a series of vinyl thionium ions generated from the corresponding allylic sulphoxides (3–6) with TMSOTf and diisopropylethylamine in CH₂Cρ at –78°C.     

Deracemization of silyl enol ethers

The deracemization by enantioselective protonation of silyl enol ethers was tested using 2,2-dimethyl 5-phenyl 1,3-dioxolan 4-one 1. The results obtained, especially with pantolactone as a chiral proton donor, are better than when the deracemization is carried out with the lithium enolate of 1.     

Stereo- and regio-selective conversion of 1-trimethylsilylallylic alcohols into the silyl enol ethers catalyzed by butyllithium

(Z)-Silyl enol ethers can be prepared selectively with complete regio-specificity by treating 1-trimethylsilylallylic alcohols with a catalytic amount of butyllithium.     

Regiospecific ureidoalkylation of silyl enol ethers

Site-specific ureidoalkylation of silyl enol ethers can be achieved by their reactions with chloromethylcarbamates at ?78° under the influence of titanium tetrachloride.     

Lewis acid-catalyzed nucleophilic substitutions of propargylic and allylic silyl ethers with enol silyl ethers

Nucleophilic reactions of various enol silyl ethers with carbocation species generated from propargyl silyl ethers by the action of a Lewis acid have been developed. The present method is highly useful for the introduction of allenic or enyne functionalities into the alpha-position of substituted ketones. [reaction--see text]     

A silver-catalyzed spirocyclization of alkynyl silyl enol ethers

Ring out the old: The cycloisomerization of alkynyl silyl enol ethers proceeds at ambient temperature under the mild conditions of silver catalysis. Mono- or bicyclic spiro compounds can be obtained by 5-exo-dig reactions. Trapping the vinyl silver species with an iodide source, such as N-iodosuccinimide (NIS), afforded the alkenyl iodide derivatives.     

Reaction of silyl enol ethers with cyanogen chloride

Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 6, pp. 1447–1448, June, 1988.     

α-Hydroxylation of ketones: Osmium tetroxide/N-methylmorpholine-N-oxide oxidation of silyl enol ethers

Osmium tetroxide/N-methylmorpholine-N-oxide oxidation of silyl enol ethers, derived from ketones with either kinetic or thermodynamic regiochemical control, produces α-ketols in good to excellent yields.     

Asymmetric oxidation of silyl enol ethers using chiral dioxiranes derived from α-fluoro cyclohexanones

Asymmetric oxidation of silyl enolethers derived from tetralone, 2-methyl-tetralone, propiophenone and deoxybenzoin using chiral dioxiranes generated in situ from oxone and new chiral α-fluorinated cyclohexanones or fructose-derived ketone have been studied. It was observed that tetrasubstituted silyl enolethers are poor substrates, that substitution at C8 of the fluoro-ketones has a significant effect on the enantioselectivities obtained and that the fructose-derived-ketone provides higher enantioselectivities. The absolute configuration of the major hydroxy ketones obtained can be rationalized using a spiro model proposed for epoxidation of olefins.     

Chemoselective oxygen-centered radical cyclizations onto silyl enol ethers

A new oxygen-centered radical cyclization onto silyl enol ethers has been developed and utilized for the synthesis of versatile siloxy-substituted tetrahydrofurans. The reactions display excellent chemoselectivity for cyclization onto the electron-rich silyl enol ether when competing terminal alkene cyclization, 1,5-hydrogen abstraction, and beta-fragmentation pathways are present. The increased chemoselectivity also allows for the synthesis of tetrahydropyrans, a challenging substrate class to access using oxygen-centered radical alkene cyclizations due to competing 1,5-hydrogen abstractions.     

Ruthenium-catalyzed oxidation of silyl ethers to silyl esters

Direct oxidation of silyl ethers to silyl esters, using RuO₄ formed in situ, is reported. The reaction was optimized to minimize formation of the corresponding carboxylic acid product whose formation pathway appears to be solvent dependent. The reaction is tolerant of halides, nitriles, nitro groups, esters, epoxides, and ketones.     

Preparation of α-trialkylsilyl ketones from α-phenylseleno derivatives via their silyl enol ethers

On treatment with metallic lithium in the presence of dimethylaminonaphthalene, trialkylsilyl enol ethers of α-phenylseleno ketones were converted into the corresponding α-trialkylsilyl ketones in good yields.     

Condensation of enol silyl ethers with 2-acetoxytetrahydrofuran and -tetrahydropyrans

Trimethylsilyl trifluoromethanesulfonate catalyzes stereoselective condensation of enol silyl ethers and 2-acetoxytetrahydrofuran or -tetrahydropyran derivatives.     

Novel peparation of silyl enol ethers from allyl alcohols

A novel synthetic method for silyl enol ethers from allyl alcohols was developed using ruthenium hydride catalyst.     

Regiocontrolled synthesis of carbocycle-fused indoles via arylation of silyl enol ethers with o-nitrophenylphenyliodonium fluoride

[formula: see text] A new, regiocontrolled synthesis of carbocycle-fused indoles has been developed. The two-step procedure involves first the regiospecific arylation of silyl enol ethers with o-nitrophenylphenyliodonium fluoride (1). Reduction of the nitro group on the aromatic ring with TiCl3 followed by spontaneous condensation of the aniline with the ketone then affords the indole products.     

Direct transformation of silyl enol ethers into functionalized allenes

The first elimination reactions of silyl enol ethers to lithiated allenes are reported. These reactions allow a direct transformation of readily available silyl enol ethers into functionalized allenes. The action of three to four equivalents of lithium diisopropylamide (LDA) on silyl enol ethers results in the formation of lithiated allenes by initial allylic lithiation, subsequent elimination of a lithium silanolate, and finally, lithiation of the allene thus formed. Starting with amide-derived silyl imino ethers, lithiated ketenimines are obtained. A variety of reactions of the lithiated allenes with electrophiles (chlorosilanes, trimethylchlorostannane, dimethyl sulfate and ethanol) were carried out. Elimination of silanolate is observed only for substrates that contain the hindered SiMe2tBu or Si(iPr)3 moiety, but not for the SiMe3 group. The reaction of 1,1-dilithio-3,3-diphenylallene with ketones provides a convenient access to novel 1,1-di(hydroxymethyl)allenes which undergo a domino Nazarov-Friedel-Crafts reaction upon treatment with p-toluenesulfonic acid.