Synthesis Of Silyl Enol Ethers Research Articles

Stereoselective Synthesis of Silyl Enol Ethers with Acylsilanes and α,β-Unsaturated Ketones.

Acylsilanes are emerging bench-stable reagents for the generation of electron-rich oxycarbenes that are difficult to access with unstable diazo compounds. Herein, we report a siloxycarbene-mediated stereoselective synthesis of silyl enol ethers through visible-light-induced intermolecular reactions between acylsilanes and α,β-unsaturated ketones. Both the solvent and low temperature are important for the success of the reaction. This approach features atomic economics, exclusive stereocontrol, and broad substrate scope. The synthetic potential of this methodology is demonstrated by gram-scale reaction and various downstream transformations including that requiring configuration purity of the silyl enol ethers.

Selective Synthesis of Z-Silyl Enol Ethers via Ni-Catalyzed Remote Functionalization of Ketones.

We report a remote functionalization strategy, which allows the Z-selective synthesis of silyl enol ethers of (hetero)aromatic and aliphatic ketones via Ni-catalyzed chain walking from a distant olefin site. The positional selectivity is controlled by the directionality of the chain walk and is independent of thermodynamic preferences of the resulting silyl enol ether. Our mechanistic data indicate that a Ni(I) dimer is formed under these conditions, which serves as a catalyst resting state and, upon reaction with an alkyl bromide, is converted to [Ni(II)-H] as an active chain-walking/functionalization catalyst, ultimately generating a stabilized η3-bound Ni(II) enolate as the key selectivity-controlling intermediate.

Hydrogen-Bond-Assisted Sequential Reaction of Silyl Glyoxylates: Stereoselective Synthesis of Silyl Enol Ethers.

A novel hydrogen-bond-assisted sequential reaction of silyl glyoxylates is described. This method provides an efficient strategy for the synthesis of silyl enol ethers with high selectivity. In these transformations, hydrogen bonds from 2-nitroethanol and its derivatives are critical to the stereochemical outcome. Both E- and Z-isomers are achieved via Henry reaction/Brook rearrangement/elimination and Henry reaction/Brook rearrangement/retro-Henry reaction/elimination processes, respectively (up to 99:1 Z-selectivity, and 9.2:1 E-selectivity).

Organosilicon Reducing Reagents for Stereoselective Formations of Silyl Enol Ethers from α-Halo Carbonyl Compounds.

Salt-free stereoselective synthesis of silyl enol ethers was achieved by treating α-halo carbonyl compounds with 2,3,5,6-tetramethyl-1,4-bis(trimethylsilyl)-1,4-dihydropyrazine. In this reaction, easily removable trimethylsilyl halides and 2,3,5,6-tetramethylpyrazine were generated as the reaction byproducts. Due to the inertness of the reaction byproducts, we found a one-pot transformation of the in situ generated silyl enol ethers into various α-functionalized carbonyls by reaction with Togni-II reagent or aldehydes.

A Solvent-Free Reaction for Silyl Enol Ethers Synthesis

Silyl enol ethers are extremely useful nucleophilic intermediates for chemical transformations because they are synthetically versatile substrates for a wide range of C–C bond-forming reactions. Here, we present a new, mild, and solvent-free procedure for the synthesis of silyl enol ethers that employs a catalytic amount of solid-supported base and an equimolar amount of N,O-(bistrimethylsilyl)acetamide as a silylating agent.

ChemInform Abstract: Asymmetric Catalysis with Ethylene. Synthesis of Functionalized Chiral Enolates.

AbstractA scalable, highly efficient catalytic and enantioselective synthesis of silyl enol ethers is elaborated.

ChemInform Abstract: Cobalt‐Catalyzed Hydrosilation/Hydrogen‐Transfer Cascade Reaction: A New Route to Silyl Enol Ethers.

AbstractA novel cobalt‐catalyzed method for the synthesis of silyl enol ethers from ketones is described.

ChemInform Abstract: Reaction of Acylsilanes with α‐Sulfinyl Carbanions: Regioselective Synthesis of Silyl Enol Ethers.

The reaction of acylsilanes with α-sulfinyl carbanions such as α-lithioalkyl sulfoxide is described. The reaction proceeds to give silyl enol ethers preferentially through the initial formation of the α-silyl alkoxide intermediates. In particular, the products derived from enolizable acylsilanes were the regio-defined silyl enol ethers that cannot be obtained by usual enolization of the corresponding unsymmetrical ketones with base.

Reaction of acylsilanes with α-sulfinyl carbanions: regioselective synthesis of silyl enol ethers

The reaction of acylsilanes with α-sulfinyl carbanions such as α-lithioalkyl sulfoxide is described. The reaction proceeds to give silyl enol ethers preferentially through the initial formation of the α-silyl alkoxide intermediates. In particular, the products derived from enolizable acylsilanes were the regio-defined silyl enol ethers that cannot be obtained by usual enolization of the corresponding unsymmetrical ketones with base.

Catalytic Formation of Silyl Enol Ethers and Its Applications for Aldol-Type Condensation and Aminomethylation Reactions

A new catalytic method for the synthesis of silyl enol ethers has been developed from the coupling reaction of ketones with CH2═CHSiMe3 by using a ruthenium hydride catalyst (PCy3)2(CO)RuHCl. The synthetic utility of silyl enol ethers was demonstrated for both Mukaiyama aldol condensation and aminomethylation reactions in forming β-hydroxyketones and β-aminoketones, respectively.

ChemInform Abstract: A Novel Synthesis of Silyl Enol Ethers from α‐Silylbenzylthiols and Carboxylic Acid Derivatives via C—C Bond Formation; Thermal Rearrangement of S‐α‐Silylbenzyl Thioesters.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

A novel synthesis of silyl enol ethers from α-silylbenzylthiols and carboxylic acid derivatives via CC bond formation; thermal rearrangement of S-α-silylbenzyl thioesters

A new procedure for the synthesis of silyl enol ethers from S-α-silylbenzyl thioesters without need for either bases or catalysts via CC bond formation is described. Solutions of S-α-silylbenzyl thioesters were simply heated at 180°C for 24 h in a sealed tube to give silyl enol ethers in good yields with high stereoselectivity. Cyclization of the dipoles generated by thermal rearrangement of the silyl group and elimination of sulfur afforded silyl enol ethers.

ChemInform Abstract: Stereoselective Synthesis of Silyl Enol Ethers via the Iridium‐Catalyzed Isomerization of Allyl Silyl Ethers.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

ChemInform Abstract: Facile Synthesis of Silyl Enol Ethers by Mg‐Promoted Coupling of Aliphatic Carbonyl Compounds with Trimethylsilyl Chloride.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Facile synthesis of silyl enol ethers by Mg-promoted coupling of aliphatic carbonyl compounds with trimethylsilyl chloride

Treatment of aliphatic carbonyl compounds with trimethylsilyl chloride with Mg turning for Grignard reaction without any pre-treatment in N,N-dimethylformamide at room temperature brought about highly facile, effective and stereoselective coupling to give the corresponding silyl enol ethers in good yields.

ChemInform Abstract: Regio‐ and Stereoselective Synthesis of Silyl Enol Ethers Using a New Base Electrogenerated from Hexamethyldisilazane.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Regio- and Stereoselective Synthesis of Silyl Enol Ethers Using a New Base Electrogenerated from Hexamethyldisilazane

The hexamethyldisilazane magnesium salt, a new base readily electrogenerated in an undivided cell fitted with a sacrificial magnesium anode, using a normally equilibrating medium (DME/15% vol HMPA mixture), exhibited a surprising regioselectivity leading to the less highly substituted silyl enol ethers from unsymmetrical ketones. This regioselectivity was not temperature dependent, but was strongly dependent on the nature and proportions of the solvent/cosolvent mixture. Moreover, the reaction was different in pure NMP, and exclusively afforded, from 2-pentanone, the new silylated aldol (56% yield) which resulted from the condensation of the less highly substituted enolate with the ketone.

ChemInform Abstract: Aziridine‐Trimethylsilyl Bromide‐Ph4SbBr System as a Novel Selective Reagent for the Synthesis of Silyl Enol Ethers from Cyclic Ketones.

AbstractThe ketones (I) are treated with trimethylsilyl bromide (II) in the presence of tetraphenylstibonium bromide.

Azilidine–Trimethylsilyl Bromide–Ph4SbBr System as a Novel Selective Reagent for Synthesis of Silyl Enol Ethers from Cyclic Ketones

Abstract Azilidine–trimethylsilyl bromide–tetraphenylstibonium bromide system is an effective reagent to produce silyl enol ethers from cyclic ketones. This had the specific selectivity to silylate cyclic ketones exclusively even in the case of coexsisting with acyclic ketones.

ChemInform Abstract: An Efficient Regio‐ and Stereoselective Synthesis of Silyl Enol Ethers.

AbstractThe methyl ketones (I) react with chlorotrimethylsilane (II) in the presence of sodium bromide and triethylamine to yield the silyl enol ethers (III) ‐ (V) with predominance of the thermodynamically controlled products (III) or (IV).