Ytterbium Triflate Research Articles

Ytterbium triflate catalyzed synthesis of β-functionalized indole derivatives

Ytterbium triflate was shown to be effective in promoting the synthesis of substituted indole derivatives starting from indole, aldehydes, and dimethyl malonate by a Yonemitsu-type three component reaction. The whole process was carried out in solvent-free conditions and furnished the desired adducts in 42–67% yield.

New thermosets obtained from bisphenol A diglycidyl ether and hydroxyl‐ended hyperbranched polymers partially blocked with benzoyl and trimethylsilyl groups

AbstractNew epoxy thermosets with improved flexibility were prepared by chemical modification of bisphenol A diglycidyl ether (DGEBA) with hyperbranched polymers (HBPs). Hydroxyl‐ended hyperbranched polyesters were modified by blocking part of the hydroxyl groups with trimethylsilyl or benzoyl groups. The curing of mixtures of DGEBA with various proportions of two modified HBPs using ytterbium triflate as cationic initiator was investigated using differential scanning calorimetry and thermomechanical analysis. The characterization of these materials was performed using several thermal analysis techniques and their morphology was investigated using electron microscopy. High proportions of HBPs reduced the glass transition temperature and the relaxed storage modulus but barely affected gelation. The overall curing shrinkage was controlled by the content of hydroxyl groups and by the changes of HBP molecular interactions during curing. The results indicated that the relative proportion and type of terminal groups play a role in the evolution of the curing and the properties of the thermosets. Hydroxyl groups promoted the covalent incorporation of the HBP to the network via hydroxyl‐induced chain‐transfer reactions, whereas benzoyl groups promoted phase separation. Formulations containing HBP blocked with benzoyl groups showed two phases connected through covalent linkages between the HBP‐rich phase and the epoxy matrix. Copyright © 2010 Society of Chemical Industry

Ytterbium Triflate Catalyzed Synthesis of Alkoxy-Substituted Donor−Acceptor Cyclobutanes and Their Formal [4 + 2] Cycloaddition with Imines: Stereoselective Synthesis of Piperidines

A new synthesis of 2-alkoxy-1,1-cyclobutane diesters and their first use in dipolar cycloadditions is reported. Both the formation of the donor-acceptor cyclobutanes and their subsequent annulation with in situ formed imines are catalyzed by Yb(OTf)(3). Cyclobutanes with carbon donor groups give piperidines with high trans stereoselectivity.

Efficient synthesis of di- and trisubstituted 2-aryloxazoles via ytterbium(III) triflate catalyzed cyclization of tertiary propargylic alcohols with aryl amides

An efficient synthetic method to prepare di- and trisubstituted 2-aryloxazoles based on Yb(OTf) 3 catalyzed cyclization of trisubstituted propargylic alcohols with aryl amides is described. The reaction was accomplished in moderate to excellent product yields and with complete regioselective control. The mechanism is suggested to involve activation of the starting alcohol by the metal catalyst that results in its ionization. Subsequent cyclization of this newly generated carbocationic species with the aryl amide then affords the oxazole. In view of the mild conditions along with the low cost, commercially availability of Yb(OTf) 3 and its high tolerance to air and moisture, the present synthetic approach offers an operationally simplistic and convenient route to this important aromatic heterocycle.

Ytterbium triflate catalyzed synthesis of chlorinated lactones

The direct synthesis of chlorolactones from differently substituted alkenoic acids, using either sodium hypochlorite or chloramine T as the source of electrophilic chlorine and ytterbium triflate hydrate as the Lewis acid is described. In both cases the reactions proceeded in good yields affording selectively five- or six-membered chlorolactones.

Z-Selective hydroamidation of terminal alkynes with secondary amides and imides catalyzed by a Ru/Yb-system

A catalyst system formed in situ from bis(2-methallyl)cycloocta-1,5-diene-ruthenium(II) [(cod)Ru(met) 2], 1,4-bis(dicyclohexylphosphino)butane (dcypb) and ytterbium(III) triflate hydrate (Yb(OTf) 3) was found to catalyze the addition of nitrogen nucleophiles to terminal alkynes under mild conditions to stereoselectively form the Z-enamide or Z-enimide products. Various secondary amides and imides could be added across the triple bond of a range of aliphatic and aromatic alkynes. The new bimetallic catalyst system sets new standards with regard to scope and selectivity for the synthesis of Z-configured anti-Markovnikov enamides.

Microwave-assisted novel synthesis of amino-thieno[3,2- b]pyridines under solvent-free conditions

In the presence of a catalytic amount of ytterbium(III) triflate and under microwave irradiation, mixtures of 2-amino-3-thiophenecarbonitriles, ketones, and silica gel afforded smoothly the corresponding amino-thieno[2,3- b]pyridine derivatives in one step. A wide variety of ketones were tested under these conditions. The reactions proceeded rapidly and afforded the desired products in good to excellent yields.

Yb(OTf)3-Promoted ZnCl2-Catalyzed Conia-Ene Reaction of Linear β-Alkynic β-Dicarbonyls

An atom-economical and solvent-free ytterbium(III) triflate promoted, zinc(II) chloride catalyzed Conia-ene method has been developed for the construction of five- to six-membered-ring carbocycles. In the presence of zinc(II) chloride and ytterbium(III) triflate, a variety of linear β-alkynic β-keto esters and β-alkynic β-diketones were cyclized under neat conditions in moderate to good yields. It is noteworthy that the selectivity toward five- or six-membered­-ring carbocycles depends on substituents at the terminal alkynes.

Mild and Efficient Method for Synthesis of Eaminones Using Ytterbium Triflate as Catalyst

A mild and efficient procedure for synthesis of β-enaminones by the condensation of β-dicarbonyl compounds and amines using ytterbium triflate [Yb(OTf)3] as catalyst is described. The catalyst can be easily recovered and reused without loss of activity.

Novel thermosets based on DGEBA and hyperbranched polymers modified with vinyl and epoxy end groups

The cationic polymerization of DGEBA with two hyperbranched polymers (HBPs) with epoxy or vinyl end groups, using ytterbium triflate as initiator, has been studied. These HBPs have been obtained from commercial Boltorn H30 of which terminal hydroxyl groups have been replaced with long aliphatic ester chains having vinyl or epoxy end groups. Differences between the HBPs added as modifiers are observed with respect to the curing kinetics, network development, properties and morphology of the cured materials. While terminal epoxy groups ease the solubility of the HBP in DGEBA and allows its covalent incorporation into the network structure, the HBP with vinyl terminal groups is only miscible at high temperature and phase-separates during curing. As a consequence, morphology and thermal–mechanical properties are strongly dependent on the HBP employed.

Ytterbium Trifluoromethansulfonate

Ytterbium trifluoromethansulfonate [Yb(OTf)3] has been widely used in organic syntheses in the last few years. [¹] Yb(OTf)3 is a strong Lewis acid [²] due to the hard character of Yb³+ ion and the presence of electron-deficient triflate in its coordination sphere. In contrast to traditional Lewis acids, such as AlCl3, BF3, TiCl4, and SnCl4, which are often used in stoichiometric amounts, only catalytic amounts of Yb(OTf)3 are necessary. Moreover it can be easily recovered and reused without loss of activity. Interestingly, Yb(OTf)3 remains catalytically active in the presence of many Lewis bases containing nitrogen, oxygen, phosphorus or sulfur atoms. The resulting water-compatibility of Yb(OTf)3 [³] is one of its well-known advantages, with respect to traditional Lewis acids that are very sensitive and easily decomposed or deactivated in the presence of small amounts of water. The most interesting point from a synthetic point of view is that Yb(OTf)3-catalyzed reactions are clean, while Yb(OTf)3 is regarded as environmentally friendly catalyst. Ytterbium triflate is prepared by heating ytterbium(III) oxide or chloride in an aqueous trifluoromethansulfonic acid solution (Scheme 1). [4] [5]

ChemInform Abstract: Catalytic Propargylation of Aldehydes with Allenyltributylstannane by Ytterbium Triflate.

Abstract The first ytterbium triflate [Yb(OTf) 3 ]-catalyzed propargylation of various aldehydes with allenyltributylstannane to afford homopropargyl alcohols in good yields is described. The present result provides a versatile tool for preparation of an array of homopropargyl alcohols from the reaction of aldehydes with allenyltributylstannane; which are known to possess low reactivity.

ChemInform Abstract: Detritylation with Ytterbium Triflate.

Abstract Ytterbium triflate catalyzes the hydrolysis of tritylamines and trityloxy compounds to the corresponding amines and alcohols under mild conditions in high yields. The reactions are conducted in tetrahydrofuran in the presence of 1 equivalent of water.

ChemInform Abstract: Ytterbium Triflate Catalyzed Reactions of Imines with a Chiral Non-racemic Silyloxypyrrole.

ChemInform 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.

Novel epoxy nanocomposite materials

The use of ytterbium triflate as a catalyst for the cure of nano modified epoxy resins is described. Incorporation of γ-valerolactone was explored as a means of reducing the fragility of the material. The cure profiles were measured using the Strathclyde curometer over the temperature window of 90 to 120°C. The gelation time was sensitive to the concentration of the catalyst present. Incorporation of nanosilica particles, created using a sol–gel method, allowed enhancement of the physical properties of the base resin matrix. The addition of γ-valerolactone influenced the cure rate and the physical properties of the matrix formed. The mechanical and thermal properties of the materials were studied using dynamic mechanical thermal analysis and differential scanning calorimetry. The incorporation of the γ-valerolactone at certain levels leads to a reduction of the glass transition temperature with increasing level of nanofiller rather than the expected increase.

New ferrocenyl-substituted heterocycles. Formation under Biginelli conditions, DFT modelling, and structure determination

A series of novel ferrocene-containing-dihydropyrimidines (DHPs) were prepared by three-component Biginelli reactions of formylferrocene, 1,3-dioxo-components and thiourea catalyzed by boric acid and ytterbium triflate, respectively. When cyclic-1,3-diones were employed as dioxo component in the reactions promoted by boric acid, besides one expected 4-ferrocenyl-2-thioxoquinazoline, 9-ferrocenyl-2 H-xanthene-1,8-dione and 9-ferrocenylcyclopenta[ b]chromen-8-ones could also be isolated as products. By means of control reactions and B3LYP/6-31 G(d) modelling the formation of the chromenone was interpreted by hetero-Diels–Alder addition involving the Knoevenagel intermediate and the cyclopentadiene resulted in situ from acid-catalyzed decomposition of formylferrocene. The enhanced tendency of the acyclic dioxo components to undergo Biginelli reaction avoiding cycloaddition was reasoned by the formation of Knoevenagel intermediates capable of chelating proton or Lewis acids. The structures of the new compounds were established by IR and NMR spectroscopy, including HMQC, HMBC, DEPT and DNOE measurements. Some structural characteristics were disclosed by B3LYP/6-31 G(d) method.

One-Pot Synthesis and Fluorescence Properties of 2-Arylquinolines

Abstract The one-pot synthesis of 2-arylquinoline with arylamines, arylaldehyde, and 1,1-diethoxyethane were studied using a catalytic amount ytterbium triflate. Various 2-arylquinolines showed fluorescence properties and the fluorescence was quenched by introducing the nitro group into aryl moiety of 2-arylquinolines.

ChemInform Abstract: Ytterbium(III) Triflate Catalyzed Tandem Friedel—Crafts Alkylation/Hydroarylation of Propargylic Alcohols with Phenols as an Expedient Route to Indenols.

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: Efficient Synthesis of Alkyl 2,3‐Unsaturated Glucopyranosides from Glycals Mediated by Ytterbium(III) Triflate—Trialkyl Aluminum.

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 new Yb3+-catalyzed pinacol and imine-coupling reaction

Abstract Ytterbium triflate, Yb(OTf) 3 , catalyzes the intermolecular reductive homocouplings of imines, aldehydes, and ketones at loadings of 5 mol % in the presence of Mg and Me 3 SiCl to give isolated yields of up to 95%. Diastereoselectivity of up to 4/96 ( dl / meso ) is achieved for aromatic aldehydes, up to 100% dl for aliphatic aldehydes, and 100% dl for an intramolecular imine coupling.