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Results 401 - 450 of 2319
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Yu Jie - - 2010
The kinetic resolution of racemic 2,3-allenoates was realized via 1,3-dipolar cycloaddition by using a bisphosphoric acid catalyst, affording the optically active 2,3-allenoates and 3-methylenepyrrolidine derivatives in high yields and enantioselectivities.
Vanková Barbora - - 2010
Solid-phase synthesis of bisheterocyclic compounds that contain purine and the 3-hydroxyquinolin-4(1H)-one skeleton connected with an aliphatic spacer of a different length/structure is described. The reaction sequence started from the primary amines immobilized on aminomethylated polystyrene resin equipped with an acid-labile linker (4-(4-formyl-3-methoxyphenoxy)butyric acid). After the arylation of amines with 2,6-dichloropurine ...
Park Kyungho - - 2010
Symmetrical diarylalkynes were obtained from propiolic acid (or 2-butynedioic acid) and aryl halides in good yields. The optimized reaction conditions were 2.0 equiv of aryl halide, 1.0 equiv of propiolic acid, 5.0 mol % Pd(PPh(3))(2)Cl(2), 10.0 mol % 1,4-bis(diphenylphosphino)butane (dppb), 2.0 equiv of 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU), and dimethyl sulfoxide (DMSO) as ...
Hashimoto Takuya - - 2010
Phase-transfer catalyzed asymmetric alkylation and Michael addition of 5-silylalkynyl-1,3-dioxolan-4-one were developed as a novel strategy to provide highly modular tertiary α-alkyl-α-hydroxy acids bearing an alkyne moiety.
Xu Chu-Pei - - 2010
We report a mild and environmentally benign method for the synthesis of tertiary amines using alcohols as the alkylating reagents. Not only secondary amines such as piperazines but also amino acids and amino alcohols can be N-alkylated selectively. For N,O-benzyl protected amino alcohols, both N,O-de-benzylation and N-methylation were achieved in ...
Weber Manuel - - 2010
Cooperative activation by a soft bimetallic catalyst, a hard Brønsted acid, and a hard Brønsted base has allowed the formation of highly enantioenriched, diastereomerically pure masked alpha-amino acids with adjacent quaternary and tertiary stereocenters in a single reaction starting from racemic N-benzoylated amino acids. The products can, for example, be ...
Uraguchi Daisuke - - 2010
Chiral diaminodioxaphosphonium salts have been developed and their unique abilities as a chiral proton have been revealed through the establishment of a highly enantioselective protonation of alpha-amino acid-derived ketene disilyl acetals.
Zamfir Alexandru - - 2010
BINOL-derived phosphoric acids have emerged during the last five years as powerful chiral Brønsted acid catalysts in many enantioselective processes. The most successful transformations carried out with chiral BINOL phosphates include C-C bond formation reactions. The recent advances have been reviewed in this article with a focus being placed on ...
Colquhoun Howard M - - 2010
Pseudoacid chlorides of 2,5-bis(4-fluorobenzoyl) terephthalic acid and 4,6-bis(4-fluorobenzoyl) isophthalic acid condense with primary amines to afford diastereomeric bis(hydroxyindolinone)s in good isolated yields and with diamines to give high molecular weight poly(hydroxyindolinone)s. Bis-N-pyrenemethyl bis(hydroxyindolinone)s assemble, even in dipolar solvents such as DMSO, with macrocyclic diimide-sulfones to give [3]pseudorotaxanes stabilized by electronically ...
Dekeukeleire Stijn - - 2010
Chiral short-chain alpha-chloroaldehydes were prepared starting from enantiomerically pure amino acids in a three-step approach, thus providing a practical synthetic alternative for known organocatalytic alpha-chlorination procedures. The latter aldehydes proved to be useful starting materials for the stereoselective Staudinger synthesis of (3S,4S)-4-[(1S)-1-chloroalkyl]azetidin-2-ones in high diastereomeric ratios and good overall yields, ...
Zhu Lvfeng - - 2010
A challenging direct asymmetric hydrogenation of (E)-2-oxo-4-arylbut-3-enoic acids to give 2-hydroxy-4-arylbutanoic acids (85.4-91.8% ee) was achieved with a Ru catalyst based on SunPhos as the chiral ligand. Further investigation of the reaction revealed that partial isomerization of 2-hydroxy-4-arylbutenoic acids was involved in the hydrogenation process. Employing the reaction conditions to ...
McNulty LuAnne - - 2010
The synthesis of cyclic alkenyl boronic half acids from vinyl and propenyl boronic esters and homoallylic alcohols by ring-closing metathesis is reported. The method is compatible with both conventional and microwave heating and comparable yields are obtained under both conditions. The cyclic alkenyl boronic acids participate in Suzuki-Miyaura coupling reactions ...
Park Nahyun - - 2010
Three different types of catalysts were evaluated for organosolv pretreatment with pitch pine (Pinus rigida). Sulfuric acid, magnesium chloride, and sodium hydroxide for acid, neutral and base catalysts, respectively, were used, and ethanol was the organic solvent. The pretreatment process was conducted at different temperatures and times. The enzymatic hydrolysis ...
Fang Ping - - 2010
A novel Pd-catalyzed decarboxylative ortho-acylation of acetanilides with alpha-oxocarboxylic acids is realized at room temperature. This reaction provides efficient access to o-acyl acetanilides under mild conditions.
Wang Lili - - 2011
In the present work, a new route for preparation of high-performance porous carbons under mild conditions was reported. The high surface area (2700 m2/g) and large pore volume (1.98 cm3/g) porous carbons were prepared from hydrochars by conventional phosphoric acid activation method. The hydrochars described here can be obtained from ...
Caglioti Luciano - - 2011
Origin(s) of biological chirality appear(s) to be intimately connected to origin(s) of life. Prebiotic evolution toward these important turning points can be traced back to single chiral molecules. These can be small (monomeric) units as amino acids or monosaccharides or oligomers as oligo-RNA type molecules. Earlier speculations about these two ...
Cheon Cheol Hong - - 2010
A new Lewis base-tolerant LBA (Lewis Acid Assisted Brønsted Acid) derived from La(OTf)(3) and (S)-HOP has been developed as a new chiral Brønsted acid. This acid has been successfully applied as a catalyst to asymmetric protonation reactions of silyl enol ethers of 2-substituted cyclic ketones.
Pousse Guillaume - - 2010
A syn-enantioselective aldol reaction has been developed using Brønsted acid catalysis based on H(8)-BINOL-derived phosphoric acids. This method affords an efficient synthesis of various beta-hydroxy ketones, some of which could not be synthesized using enamine organocatalysis.
Spengler Jan - - 2010
An efficient strategy to synthesize tartaric acid building blocks for totally regioselective transformations or derivatizations was disclosed. Starting from l-tartaric acid or l-dimethyl tartrate, respectively, we obtained type I and II building blocks with orthogonal sets of protecing groups (4-8 steps, 38-56% overall yield).
Yang Chun-Ming - - 2010
A highly regio- and stereoselective nickel-catalyzed three-component coupling of alkynes with enones and alkenyl boronic acids to afford highly substituted 1,3-dienes is described. The reaction can also be extended to cyclization of enynes with coupling to alkenyl boronic acids. A possible reaction mechanism involving a five-membered nickelacycle as a key ...
Bayer Sally - - 2011
Several novel nitrilases were selected from metagenomic libraries using cinnamonitrile and a mixture of six different nitriles as substrates. The nitrilase gene nit1 was expressed in Escherichia coli and the resulting protein was further examined concerning its biochemical properties. Nit1 turned out to be an aliphatic nitrilase favoring dinitriles over ...
Zhang Yansheng - - 2011
Artemisinin, in the form of artemisinin-based combination therapies (ACTs), is currently the most important compound in the treatment of malaria. The current commercial source of artemisinin is Artemisia annua, but this represents a relatively expensive source for supplying the developing world. In this study, the possibility of producing artemisinin in ...
Socha Aaron M - - 2010
We report that catalytic quantities of the Lewis acidic metal catalysts scandium triflate and bismuth triflate promote conversion of oleic, linoleic, palmitic and myristic acids and their glyceryl triesters to the corresponding methyl esters (biodiesel) in greater than 90% yield upon microwave heating. Additionally, both catalysts could be recovered and ...
Wu Yen-Ku - - 2010
Treatment of siloxy enynes with base leads to the corresponding vinylsiloxyallenes which undergo Nazarov cyclization in the presence of trifluoroacetic acid to provide the cyclized product as a mixture of regioisomers in moderate to good overall yield.
Li Mingzong - - 2010
An efficient palladium-catalyzed decarboxylative acylation of unactivated arenes with alpha-oxocarboxylic acids is reported. This method provides a novel access to aryl ketones.
Wang Guowei - - 2010
The combined Lewis acid catalytic system, generated from (R)-1,1'-bi-2-naphthol [(R)-BINOL], Ti(O-i-Pr)(4), H(2)O, and lithium chloride, effectively catalyzed the enantioselective vinylogous aldol reaction of Brassard's diene with aromatic aldehydes affording the (Z)-delta-hydroxyl-alpha,beta-unsaturated esters exclusively in good yields with excellent enantioselectivities (90-99% ee) under mild conditions. A Lewis acid-Lewis acid bifunctional working ...
Luo Fang - - 2010
A copper(I)-catalyzed bis-esterification of cyclic anhydrides with aryl and vinyl alkoxysilanes is described, in which the alkoxy and aryl (or vinyl) esters of dicarboxylic acids were prepared in one pot with moderate to good yields. Notably, vinyl trimethoxysilanes also worked well with this procedure.
Downey C Wade - - 2010
In the presence of TMSOTf and a trialkylamine base, acetic acid undergoes aldol addition to non-enolizable aldehydes under exceptionally mild conditions. Acidic workup yields the beta-hydroxy carboxylic acid. The reaction appears to proceed via a three-step, one-pot process, including in situ trimethylsilyl ester formation, bis-silyl ketene acetal formation, and TMSOTf-catalyzed ...
Merlani Maia - - 2010
The racemic and enantioselective synthesis of a novel glyceric acid derivative, namely, 2,3-dihydroxy-3-(3,4-dihydroxyphenyl)-propionic acid as well as the antioxidant activities is described. The virtually pure enantiomers, (+)-(2R,3S)-2,3-dihydroxy-3-(3,4-dihydroxyphenyl)-propionic acid and (-)-(2S,3R)-2,3-dihydroxy-3-(3,4-dihydroxyphenyl)-propionic acid were synthesized for the first time via Sharpless asymmetric dihydroxylation of trans-caffeic acid derivatives using the enantiocomplementary catalysts, (DHQD)(2)-PHAL ...
Priatni S - - 2010
The objective of this study was to identify the Fatty Acid Methyl Ester (FAME) from Neurospora intermedia N-1 that isolated from Indonesian red peanut cake (oncom). FAME profiles have been used as biochemical characters to study many different groups of organisms, such as bacteria and yeasts. FAME from N. intermedia ...
Hirata Yasuhiro - - 2010
Cyanoformates and cyanoformamides are found to add across alkynes by nickel/Lewis acid (LA) cooperative catalysis to give beta-cyano-substituted acrylates and acrylamides, respectively, in highly stereoselective and regioselective manners. The resulting adducts serve as versatile synthetic building blocks through chemoselective transformations of the ester, amide, and cyano groups as demonstrated by ...
Raup Dustin E A - - 2010
Enzymes are a continuing source of inspiration for the design of new chemical reactions that proceed with efficiency, high selectivity and minimal waste. In many biochemical processes, different catalytic species, such as Lewis acids and bases, are involved in precisely orchestrated interactions to activate reactants simultaneously or sequentially. This type ...
Liang Zunjun - - 2010
Mild conditions have been developed to achieve a Pd(OAc)(2)-catalyzed cross-coupling between indoles and arylsiloxanes in the presence of TBAF and Ag(2)O in acidic medium. Electron-deficient arylsiloxanes presented high efficiency in this system to give the arylated indoles in excellent yields.
Medeiros Matthew R - - 2010
Substituted dihydropyrans, easily accessed from a commercially available glycal, undergo acid-catalyzed rearrangement to provide highly functionalized isochroman and dioxabicyclooctane scaffolds.
Mirri Giorgio - - 2010
A chiral ferrocene-based boronic acid interacts with (R)- and (S)-Binol to form two complexes that exhibit significantly different ferrocene-based electrode potentials. This difference in redox behavior can be exploited to demonstrate in principle how high levels of enantiomeric excess in a mixture of enantiomers can be quantified and read-out using ...
Hodgson David M - - 2010
Reaction of diazodiketoesters 17 and 28 with methyl glyoxylate in the presence of catalytic rhodium(II) acetate generates predominantly the 6,8-dioxabicyclo[3.2.1]octanes 29 and 30, respectively. Acid-catalysed rearrangement of the corresponding alcohol 31 favours, at equilibrium, the 2,8-dioxabicyclo[3.2.1]octane skeleton 33 of the squalestatins-zaragozic acids. Force field calculations on the position of the ...
Kokatla Hari Prasad - - 2010
New syntheses of (-)-deoxoprosophylline, (+)-2-epi-deoxoprosopinine, and (2R,3R)- and (2R,3S)-3-hydroxypipecolic acids are reported. Utilization of the chiral functionalities of Perlin aldehydes, derived from 3,4,6-tri-O-benzyl glycals, has been done along with chemoselective saturation of olefins and reductive aminations as key steps.
Fustero Santos - - 2010
Chiral imino lactones derived from (R)-phenylglycinol containing an allyl- or propargyltrimethylsilyl group in the side chain readily cyclized in the presence of acidic reagents to afford spirocyclic compounds with high diastereoselectivity. Removal of the chiral auxiliary produced 2-substituted 1-aminocycloalkanecarboxylic acids, whereas further cyclizations by means of metathesis or hydroamination reactions ...
Dupré Nathalie - - 2010
The preparation of new organosoluble Lewis acidic polyoxometalates (POMs) is reported. These complexes were prepared by the incorporation of Zr, Sc, and Y atoms into the corresponding monolacunary Dawson [P(2)W(17)O(61)](10-) and Keggin [PW(11)O(39)](7-) polyoxotungstates. The catalytic activity of these compounds was evaluated for C-C bond formation in the Diels-Alder, Mannich, ...
Spitler Eric L - - 2010
Covalent organic frameworks (COFs) offer a new strategy for assembling organic semiconductors into robust networks with atomic precision and long-range order. General methods for COF synthesis will allow complex building blocks to be incorporated into these emerging materials. Here we report a new Lewis acid-catalysed protocol to form boronate esters ...
Belitsky Jason M - - 2010
Inhibitors of melanin formation are sought after for a range of applications. Boronophenylalanine is known to inhibit melanogenesis via boronic acid-catechol interactions. A spectroscopic assay was developed to study the polymerization of l-dopa to synthetic melanin in the presence of para-substituted aryl boronic acids. The best inhibition was observed for ...
Lewandowski Bartosz - - 2010
C(2)-Symmetrical chiral macrocycles containing two sucrose units were prepared by an amino acid templated macrocyclization reaction between appropriate sucrose-based linear precursors and ethylenediamine.
Gourdet Benoit - - 2010
Annulation of ynamides with arylboronic acids or esters containing an electrophilic functional group at the ortho-position proceeds under the action of rhodium catalysis to generate 2-amidoindenols or 2-amidoindenes, usually with good regioselectivity.
Al-Zoubi Raed M - - 2010
A convenient and regioselective silver(I)-mediated electrophilic iodination and bromination reaction of arylboronic acids has been developed. The boronic acid does not require protection prior to the reaction, which can be performed on a multigram scale with moderate to excellent yields. A mild, simple, and effective method is disclosed to provide ...
Schneider Uwe - - 2010
In(I)OTf has been uncovered as an effective Lewis acid catalyst for unprecedented nucleophilic substitution of acetals or ketals with allylboronates. A transmetalative S(N)1 mechanism is proposed in which a single In(I) center acts as a dual catalyst to activate both reagents sequentially. Contrary to the classic gamma-selectivity of allylsilanes (Hosomi-Sakurai ...
Jiang Min - - 2010
Lewis acid catalyzed cycloaddition of methylenecyclopropanes (MCPs) with o-quinonemethide analogues, derived from the corresponding salicylaldehydes and CH(OEt)(3), produces the corresponding cycloadducts 3 in moderate to high yields at room temperature (20 degrees C). Moreover, the compounds 3 can be transformed to the indene derivatives 5 at high temperature. Plausible mechanisms ...
Tsui Gavin Chit - - 2010
A novel regioselective rhodium(I)-catalyzed hydroarylation of unactivated alkenes with arylboronic acids is described. The catalytic system employs [Rh(COD)OH](2) and BINAP to effect the addition of various arylboronic acids to protected allylic amines. The regioselectivity was found to be highly dependent on the protecting group, favoring the linear addition product with ...
Fernández-Trillo Francisco - - 2010
The use of natural amino acids as chiral ligands on a triethylbenzene scaffold for the binding and enantiodifferentiation of carbohydrates has resulted in moderate affinity and selectivity values for glucose. Selective 1D TOCSY experiments revealed this as a powerful titration technology surpassing the severe overlapping of receptor and carbohydrate signals ...
Park Chan Pil - - 2010
A palladium-catalyzed diacetoxylation of alkenes in the presence of peracetic acid and acetic anhydride was developed to produce diacetates efficiently and diastereoselectively. Due to its mild conditions, this method was suitable for a broad range of substrates encompassing conjugated and nonconjugated olefins.
Zhang Qiang - - 2010
An efficient and facile gold-catalyzed three-component tandem process for the assembly of two types of highly functionalized butenolides has been developed. In this reaction system, more than four chemical bonds are formed by a single gold catalyst. The present tandem protocol includes a direct coupling of alkynes, amines, and glyoxylic ...
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