Oxidative carbon-carbon bond formation via silyl bis-enol ethers: controlled cross-coupling for the synthesis of quaternary centers

Unsymmetrical silyl bis-enol ethers have been developed as effective substrates for synthesizing quaternary centers from tetralone derivatives through oxidative carbon-carbon bond formation. The derived products are shown to be highly versatile intermediates that may be used to generate diverse structures such as cyclopentenones, 2H-pyrroles, and spirocyclic pyrrolidines.     

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.     

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.     

Effect of fluorine on palladium-catalyzed cross-coupling reactions of aryl bromides with trifluoromethyl aryl ketones via difluoroenol silyl or monofluoroenol silyl ethers

Palladium-catalyzed cross-coupling reactions of alpha-aryl-beta,beta-difluoroenol silyl and alpha-aryl-beta-fluoroenol silyl ethers with aryl bromides proceed smoothly with good functional compatibility.     

Nickel-catalyzed cross-coupling of silyl enol ethers with grignard reagents. Regio- and stereocontrolled synthesis of olefins

The substitution of the siloxy group in silyl enol ethers with Grignard reagents to form olefins is accomplished by use of nickel acetylacetonate or phosphine-nickel complexes as catalysts, the stereo- and regiochemistry of coupled olefins depending upon the nature of the catalyst and reaction conditions employed.     

Oxidative nucleophilic substitution of hydrogen in nitroarenes by silyl enol ethers

Enolates generated by treatment of silyl ketene acetals and enol ethers with fluoride ion sources add to nitroarenes to produce σ^H adducts that oxidize either with KMnO₄ to give substituted nitroarenes or with dimethyldioxirane to give substituted phenols. In the latter case the oxidation results in replacement of the nitro group with a hydroxy group. It was shown that high effectiveness of these reactions is not due to stabilization of the σ^H adducts via O-silylation but due to the nature of the accompanying cation.     

Catalytic isomerization of acetylenic silyl ethers to dienol silyl ethers by ruthenium hydride complexes

Acetylenic silyl ethers are converted catalytically to the corresponding conjugated dienol silyl ethers by ruthenium hydride complexes.     

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]     

Tetrabutylammonium phenoxide induced reaction of silyl nucleophiles

Reaction of silyl dithiolanes with electrophiles can be efficiently promoted by catalytic amounts of tetrabutylammonium phenoxide (PhONn-Bu₄), leading to a convenient access to functionalized dithiolanes. PhONn-Bu₄ proved effective also in promoting reactions of silylated sulfides such as PhSTMS and HMDST as well as silylated selenides such as PhSeTMS and HMDSS toward epoxides. The present reactivity is also observed on using ILs as reaction media.     

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.     

Anionic rearrangements starting with 1-lithio-2-propynyl silyl ethers a route to (β-trimethylsilylvinyl) silyl ketones

The title compounds undergo silyl-Wittig rearrangement at low temperature and lead to allenolates at room temperature.     

Reaction of silyl enol ethers with cyanogen chloride

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

Reactions of enol silyl ethers with N-halosuccinimide - a stepwise process

The N-chlorosuccinimide (NSC) reaction of a number of cyclic and acyclic trimethylsilyl enol ethers was investigated. Based on product analyses, the mechanism of the reaction is postulated to involve a step-wise process.     

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.     

Preparation of silyl polyenol ethers by carbonyl olefination of silyl esters

Silyl enol ethers were produced by the carbonyl olefination of silyl esters with titanium carbene complexes generated by the desulfurizative titanation of thioacetals. The regioselective preparation of silyl dienol and trienol ethers has been achieved by using unsaturated silyl esters and thioacetals.     

A novel rearrangement leading to methoxycarbonylmethylated silyl enol ethers

Methyl 2-siloxycyclopropanecarboxylates rearrange smoothly and quantitatively to the corresponding silyl enol ethers (3) by addition of a catalytical amount of iodo trimethylsilane. Scope and limitation of this novel process as well as the synthesis of the electron rich diene (10a) are described.     

Enantioselective organocatalytic Mukaiyama-Michael addition of silyl enol ethers to alpha,beta-unsaturated aldehydes

[reaction: see text] A highly enantioselective, organocatalytic Mukaiyama-Michael addition reaction of silyl ethers and alpha,beta-unsaturated aldehydes has been developed. The process, catalyzed by MacMillan's chiral imidazolidinone, affords delta-keto aldehydes in high yields (56-87%) and high enantioselectivities (85-97% ee). Moreover, the reaction is applicable to a wide range of silyl ethers and alpha,beta-unsaturated aldehydes and, as such, provides access to a range of important synthetic building blocks.