Zn-mediated rhodium-catalyzed α-trifluoromethylation of ketones via silyl enol ethers

The treatment of silyl enol ethers of ketones with CF₃-I and Et₂Zn in the presence of RhCl(PPh₃)₃ in DME gave α-trifluoromethyl ketones in good yields. The reaction can be widely applicable to silyl enol ethers derived from aliphatic or aromatic ketones. In the absence of the rhodium catalyst, the reaction was very slow and the yields were quite poor.     

Synthesis of enantiopure homoallylic ethers by reagent controlled facial selective allylation of chiral ketones

The stereoselective allylation of chiral methyl ketones to give tertiary homoallylic ethers, which can easily be transformed into homoallylic alcohols, is described. Reaction of the enantiopure ketones 8a-d and the racemic ketones 26a-d with the norpseudoephedrine derivative 2 or ent-2 and allylsilane in the presence of a catalytic amount of trifluoromethanesulfonic acid, led to a series of homoallylic ethers with good to excellent diastereoselectivity (85:15 to > 97:3). The allylation is reagent controlled and nearly independent from the stereogenic centers in the substrates. A partial kinetic resolution was observed using the racemic ketones 26a-d. In the reaction of the chiral ketones 8a-d with the achiral reagents ethoxytrimethylsilane and allylsilane only a low diastereoselectivity was observed.     

A novel aminomethylation of silyl enol ethers with aminomethyl ethers catalyzed by iodotrimethylsilane or trimethylsilyl trifluoromethanesulfonate

The iodotrimethylsilane-catalyzed reaction of silyl enol ethers with aminomethyl ethers in acetonitrile gives aminomethylation products of the corresponding ketones readily. The reaction can slso be catalyzed by trimethylsilyl trifluoromethanesulfonate in dichloromethane.     

Catalytic asymmetric hydrosilylation of ketones: I. Chiral phosphine-platinum(II) complex-catalyzed hydrosilylation.

Dichlorobis(dimethylphenylphosphine)di-μ-chlorodiplatinum(II) was found to be an effective catalyst for the hydrosilylation of alkyl phenyl ketones with methyldichlorosilane to give the corresponding silyl ethers of 1-phenylalkanols. In the case of dialkyl ketones, the reaction was accompanied by formation of silyl enol ethers in considerable amounts. Asymmetric hydrosilylation of a series of alkyl phenyl ketones catalyzed by chiral phosphine- platinum(II) complexes was undertaken. The products were readily converted into partially active 1-phenylalkanols.     

Selenium stabilized carbenium ions. Lewis acid mediated seleno-alkylation of ketones.

Silyl enol ethers of ketones can be successfully selenoalkylated by Lewis acid activated seleno-ketals; the product β-seleno-ketones undergo interesting oxidation-deselenation reactions.     

DDQ-mediated direct cross-dehydrogenative-coupling (CDC) between benzyl ethers and simple ketones

A direct Cross-Dehydrogenative-Coupling (CDC) between benzyl ethers and simple ketones was developed without using any metal catalyst. By using DDQ, various benzyl ethers and simples ketones were coupled together directly to form beta-alkoxyl ketones efficiently. A mechanism in which the DDQ serves the double roles of an oxidizing agent and an organomediator was proposed.     

Synthesis of Silicon-Functionalized Dimethylsilyl Enol Ethers from Ketones

Symmetrical dimethylsilyl bis-enol ethers are obtained in good yield by reaction of ketones with dichlorodimethylsilane in the presence of triethylamine and sodium iodide. Reaction of ketones with N, N - diethylaminodimethylchlorosilane in the presence of triethylamine and sodium iodide followed by subsequent conversions provides a useful synthesis of silicon-functionalized dimethylsilyl enol ethers including unsymmetrical dimethylsilyl bis-enol ethers     

17O-RMN. d'éthers,de cétones et d'esters cycliques. Détermination de constante de couplage quadrupolaire

¹³C- and ¹⁷O-relaxation times measured in cyclic ethers, cyclic ketones, and lactones allowed the determination of the quadrupolar interaction at the O-site. Values obtained for six-membered rings can be used as standard values for ethers (χ = 13 MHz), ketones (χ = 10.5 MHz), and esters (χ = 11.5 MHz for dicoordinated and 9.5 MHz for monocoordinated O-atom). Even within a series, no correlation is found between the ¹⁷O-chemical shift and the value of quadrupolar interaction.     

One-step ethynylation of silyl enol ether with chlorosilylethyne

[reaction: see text] In the presence of GaCl(3), silyl enol ethers are ethynylated at the alpha-carbon atom with chlorotrimethylsilylethyne. This reaction can provide alpha-ethynylated aryl ketones possessing acidic alpha-protons without isomerization to conjugated allenyl ketones.     

Lead(IV) acetate mediated cleavage of β-hydroxy ethers: enantioselective synthesis of α-acetoxy carbonyl compounds

α-Acetoxy aldehydes or α-acetoxy ketones can be efficiently synthesized by treating 2,3-epoxy primary alcohols with lead tetraacetate. The reaction, which proceeds with complete regio- and stereoselectivity facilitates the enantioselective synthesis of α-acetoxy carbonyl compounds from allyl alcohols, via Sharpless epoxidation. Cyclic β-hydroxy ethers, with an oxygenated five-, six- or seven-membered ring, are transformed into α-acetoxy ethers.     

Nucleophilic addition to iminium ethers in the preparation of functionalized N-alkyl heterocycles

Bicyclic iminium ethers can be synthesized by the reactions of ketones with hydroxyalkyl azides. These cationic species react with a variety of nucleophiles via two possible pathways. The initially formed, kinetic product arises from direct addition to the iminium carbon in the substrate. In some cases, the initial adduct reverts to the starting iminium ether and the ultimate product arises from nucleophilic displacement at the O-alkyl group to afford the terminally functionalized N-substituted amide. The behavior of a range of nucleophiles was studied by using several iminium ethers. In general, the relevant pathway could be identified by characterization of the product formed. For hydroxide addition, which can afford only one product regardless of mechanism, the reaction was shown to arise by the kinetic pathway, using (18)O-labeled hydroxide. A one-pot synthesis of functionalized lactams entailing treatment of ketones first with hydroxyalkyl azides followed by nucleophilic addition was also developed.     

Sulfuric Acid Adsorbed on Silica Gel. A Multipurpose Acid Catalyst

A series of acid catalyzed reactions like the dehydration of alcohols, conversion of ketones to 1,3-dioxolanes and their hydrolysis, α,β-unsaturated ketones to enol ethers, and alcohols to methyl-methoxyethyl ethers are performed efficiently in high yield with sulfuric acid adsorbed on silica gel as catalyst.     

Acetal,triphenyl phosphorane,enol ether,acidic hydrolysis,nitroxyl

Two acetals were synthesised with hydroxymethyl triphenylphosphonium chloride as the alcoholic component. Reaction with ketones in the Wittig synthesis yielded enol ethers which were hydrolysed to aldehydes under acid catalysis. Tetrahydropyranyloxy compounds could be hydrolysed under milder conditions whereas, methoxymethyl ethers needed slightly more drastic conditions than the methyl ethers normally used in this synthesis.     

A review of Mg metal-promoted CF bond activation; a reliable synthetic approach to difluorinated organic compounds

The carbon-fluorine bond of a trifluoromethyl group attached to a π system can be activated by metallic magnesium in the system TMSCl-THF or DMF providing a variety of difluorinated compounds via a selective CF bond cleavage. Thus, trifluoromethyl ketones, α,β-unsaturated ketones, esters, imines, and aromatics can be transformed into the corresponding difluoroenol silyl ethers, enamines, and difluoro(trimethylsilyl)methyl aromatics in good to excellent yields, respectively. This protocol enabled us to synthesize β,β-difluoroamino acids, difluoroheterocycles, and functionalized difluoroacetates.     

Radical trifluoromethylation of ketone silyl enol ethers by activation with dialkylzinc

[reaction: see text] The radical trifluoromethylation of ketone silyl enol ethers gave alpha-CF(3) ketones in good yields with wide scope of the ketonic substrates including acyclic ketones and cyclopentanone. The use of dialkylzinc to activate the silyl enol ethers is the key to the efficient radical trifluoromethylation.     

2-iodylphenol ethers: preparation, X-ray crystal structure, and reactivity of new hypervalent iodine(V) oxidizing reagents

2-Iodylphenol ethers were prepared by the dimethyldioxirane oxidation of the corresponding 2-iodophenol ethers and isolated as chemically stable, microcrystalline products. Single-crystal X-ray diffraction analysis of 1-iodyl-2-isopropoxybenzene 8c and 1-iodyl-2-butoxybenzene 8d revealed pseudopolymeric arrangements in the solid state formed by intermolecular interactions between IO2 groups of different molecules. 2-Iodylphenol ethers can selectively oxidize sulfides to sulfoxides and alcohols to the respective aldehydes or ketones.     

The breakdown of vinyl ethers as a two-center synchronous reaction

The experimental data on the molecular decomposition of vinyl ethers of various structures to alkanes and the corresponding aldehydes or ketones in the gas phase were analyzed using the method of intersecting parabolas. The enthalpies and kinetic parameters of decomposition were calculated for 17 reactions. The breakdown of ethers is a two-center concerted reaction characterized by a very high classical potential barrier to the thermally neutral reaction (180–190 kJ/mol). The kinetic parameters (activation energies and rate constants) of back reactions of the formation of vinyl ethers in the addition of aldehydes or ketones to alkanes were calculated using the method of intersecting parabolas. The factors that influenced the activation energy of the decomposition and formation of ethers were discussed. Quantum-chemical calculations of several vinyl ether decomposition reactions were performed. Ether formation reactions were compared with the formation of unsaturated alcohols as competitive reactions, which can occur in the interaction of carbonyl compounds with alkenes.     

Regiochemical aspects in the reaction of 2,3,5-tri-o-benzoyl-d-ribofuranosyl : Acetate with silyl enol ethers catalyzed by stannic chloride

In the reaction with silyl enol ethers catalyzed by stannic chloride, 2,3,5-tri-O-benzoyl-D-ribofuranosyl acetate behaves as an ambident electrophile; silyl enol ethers of ketones having α-hetero substituents afford C-1 adducts, whereas those of usual acyclic ketones give products arising from attack on C-2 benzoxyl group.     

Chiral Brønsted acid from a cationic gold(I) complex: catalytic enantioselective protonation of silyl enol ethers of ketones

A chiral Br?nsted acid has been developed from a cationic gold(I) disphosphine complex in the presence of alcoholic solvent and applied to the enantioselective protonation reaction of silyl enol ethers of ketones. Various optically active cyclic ketones were obtained in excellent yields and high enantioselectivities, including cyclic ketones bearing aliphatic substrates at the α-position. Furthermore, the application of this Br?nsted acid was extended to the first Br?nsted acid-catalyzed enantioselective protonation reaction of silyl enol ethers of acyclic substrates, regardless of their E/Z ratio.     

Synthesis of α-Telluroketones

α-Telluroketones were prepared by reacting 4-methoxyphenyltellurium trichloride either with ketones or silyl enol ethers of ketones. The products upon pirolysis furnish α-chloro ketones.