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Short Reaction Time (short + reaction_time)
Kinds of Short Reaction Time Selected AbstractsDynamic Enzymatic Kinetic Resolution of Methyl 2,3-Dihydro-1H -indene-1-carboxylateEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 35 2009Jörg Pietruszka Abstract A new reaction setup for kinetic enzymatic resolution was established and is demonstrated for the case of the hydrolase-catalysed conversion of methyl 2,3-dihydro-1H -indene-1-carboxylate (1) in conjunction with a base-catalysed racemisation. The system allows controlled racemisation, resulting in efficient dynamic kinetic resolution (DKR) of the title compound. Short reaction times and high enantioselectivities were obtained with CAL-B and TBD (1,5,7-triazabicyclo[4.4.0]dec-5-ene). Compound (R)- 1 (ee 95,%) served as a starting material in a domino reaction that led to the biaryl indanyl ketone (R)- 8, a lead compound for novel inhibitors of peptidyl-prolyl- cis/trans -isomerases, in 94,% ee. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) [source] The transient nature of maximum maleic anhydride grafting of polypropylene: A mechanistic approach based on a consecutive reaction model.JOURNAL OF APPLIED POLYMER SCIENCE, Issue 1 2007Abstract This article compares the batch solution and molten state chemical modification of an atactic polypropylene to yield a grafted polypropylene. Short reaction times appear to be sufficient and indeed necessary for the highest graft yields to be obtained if degradative processes occurring in both reaction media are to be avoided. The consecutive reactions for the optimized grafting reaction pathway were proposed for the solution process in an earlier article. The present work attempts to correlate this pathway with that of the molten state process. Grafted succinic anhydride groups react with two resorcine molecules to yield grafted succinyl-fluorescein groups. This work considers the resorcine units as true molecular probes, to be able to stabilize and activate the complexes formed between the succinic anhydride groups and the propylene sequence. This work shows the unsteady and later dynamic character of the process. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 345,351, 2007 [source] Straightforward Synthesis of ,-Substituted Prolines by Cross-MetathesisEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 16 2008Marco Lumini Abstract The synthesis of several ,-substituted N -Boc-protected prolines has been achieved by cross metathesis (CM) of N -Boc-allylproline 5 with terminal long chain alkenes and alkenes bearing hydroxy, silyloxy, ester, and O -acetylglucosamido groups. The CM occurred with good selectivity and short reaction time under microwave heating conditions, affording yields in the range of 40,92,%. Addition of Ti(OiPr)4 as a Lewis acid allowed a slight increase of the yield in the case of alkenes with Lewis basic substituents. The CM was also successfully applied to allylproline protected with trichloroacetaldehyde 4, but the intermediate products were less practical for further deprotection and elaboration. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source] A Remarkable Titanium-Catalyzed Asymmetric Strecker Reaction using Hydrogen Cyanide at Room TemperatureADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 13 2010Balamurugan Ramalingam Abstract Close to perfect enantioselectivity (up to 98% ee) is obtained for the formation of amino nitriles using hydrogen cyanide (HCN) as the cyanide source at room temperature for the first time. In an operationally simple process, the catalyst generated from a partially hydrolyzed titanium alkoxide (PHTA) and (S)- N -salicyl-,-amino alcohol ligand, catalyzes the cyanation of imines in a short reaction time. [source] Microwave-Assisted Dieckmann Reaction: Efficient One-Step Synthesis of 2-Aroylbenzofuran-3-olsADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 11-12 2010Zhong-Zhen Zhou Abstract This paper describes the first efficient one-step synthesis of 2-aroylbenzofuran-3-ols from the microwave-assisted Dieckmann reaction of substituted methylsalicylates with 2-bromo-1-aroylethanones in alkaline aprotic solvents. This method features excellent yields, short reaction time (15,min) and high functional group compatibility, making it an efficient and practical approach for the synthesis of 2-aroylbenzofuran-3-ols. [source] Highly Enantioselective Michael Addition of Cyclic 1,3-Dicarbonyl Compounds to ,,,-Unsaturated ,-Keto EstersADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 10 2010Xing-Kuan Chen Abstract A highly enantioselective Michael addition of cyclic 1,3-dicarbonyl compounds to ,,,-unsaturated ,-keto esters catalyzed by amino acid-derived thiourea-tertiary-amine catalysts is presented. Using 5,mol% of a novel tyrosine-derived thiourea catalyst, a series of chiral coumarin derivatives were obtained in excellent yields (up to 99%) and with up to 96% ee under very mild conditions within a short reaction time. [source] Design and Application of 2,2-Dibromodimedone as Organic Brominating Reagent for Asymmetric Bromination of 1,3-Dicarbonyl Compounds and Ketones Catalysed by Chiral Amino AcidsADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 10 2009Papori Goswami Abstract A green and ecofriendly enantioselective ,-bromination of carbonyl and 1,3-dicarbonyl compounds is reported involving the synthesis of a novel organic brominating source. The organic brominating reagent can be recovered after each cycle, rebrominated and reused. The reaction is catalysed by chiral amino acids and completed within a short reaction time with good enantioselectivity and exclusive formation of only ,-monobrominated carbonyl compounds. [source] Enantioselective Silylcyanation of Aldehydes and Ketones by a Titanium Catalyst Prepared from a Partially Hydrolyzed Titanium Alkoxide and a Schiff Base LigandADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 10 2009Kazuhiko Yoshinaga Abstract In the presence of small amount (0.2,1.0 mol%) of a titanium complex catalyst prepared from a partially hydrolyzed titanium alkoxide and an optically active tridentate Schiff base ligand, the enantioselective silylcyanation of aldehydes and ketones proceeded in a short reaction time at room temperature to afford the corresponding optically active cyanohydrin derivatives in excellent chemical yield with high enantiomeric excess (86,97% ee). The results indicate that partially hydrolyzed titanium alkoxides are a promising titanium source for the preparation of efficient catalysts for asymmetric synthesis. [source] A General and Efficient Method for the Preparation of ,-Enamino Ketones and Esters Catalyzed by Indium TribromideADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 1-2 2006Zhan-Hui Zhang Abstract A variety of ,-enamino ketones and esters have been synthesized in high to exellent yields by reacting ,-dicarbonyl compounds with amines in the presence of a catalytic amount of indium tribromide. The reaction proceeds smoothly at room temperature in a short reaction time under solvent-free conditions. [source] Synthesis of 14-aryl-14H -dibenzo[a,j]xanthenes catalyzed by acyclic acidic ionic liquidsJOURNAL OF HETEROCYCLIC CHEMISTRY, Issue 3 2010Dong Fang Some recyclable acyclic SO3H-functionalized ionic liquids have been used as novel catalysts for the synthesis of 14-aryl-14H -dibenzo[a,j]xanthenes via the one-pot condensation of ,-naphthol and aromatic aldehydes in aqueous medium. The condensation reaction was accomplished successfully with various aromatic aldehydes with good to excellent yields ranged from 86 to 96% within 5,30 min. After the reaction, the products could simply be separated from the catalysts by filtration. When separated from the reaction mixture, the catalysts could be recycled and reused for several times without noticeably reducing catalytic activity. The methodology gives the advantages of high yields, short reaction time, and easy work-up procedure. J. Heterocyclic Chem., (2010). [source] SnCl2 · 2H2O-catalyzed one-pot synthesis of 4(3H)-quinazolinones from anthranilic acid, ortho esters, and amines under solvent free conditionsJOURNAL OF HETEROCYCLIC CHEMISTRY, Issue 2 2010Min Wang A simple, efficient, and green procedure for the one-pot synthesis of 4(3H)-quinazolinones by three components condensation of anthranilic acid, ortho esters, and amines in the presence of SnCl2 · 2H2O has been developed. The reaction occurred within short reaction time at room temperature under solvent-free conditions to afford the title products in excellent yields. J. Heterocyclic Chem., (2010). [source] A green and efficient synthesis of 3,3,-arylidenebis[4-hydroxy-6-methyl-2(1H)-3-pyridinone]s in water under microwave irradiationJOURNAL OF HETEROCYCLIC CHEMISTRY, Issue 1 2010Feng Shi A series of 3,3,-arylidenebis[4-hydroxy-6-methyl-2(1H)-3-pyridinone]s were synthesized via three-component reactions of aromatic aldehydes, 4-hydroxy-6-methyl-2H -pyran-2-one, and ammonium acetate in water under microwave irradiation. This method has the advantages of environmental friendliness, short reaction time, high yields, and easy operation. This efficient synthesis not only offers an economical and green synthetic strategy to this class of significant compounds but also enriches the investigations on microwave-assisted synthesis in water. J. Heterocyclic Chem., (2010). [source] Facile, efficient, and eco-friendly synthesis of benzo[b]pyran-2-imines over MgO and transformation to the coumarin derivativesJOURNAL OF HETEROCYCLIC CHEMISTRY, Issue 6 2009Hassan Valizadeh Room temperature synthesis of benzo[b]pyran-2-imine derivatives via the Knoevenagel condensation of malononitrile and cyanoacetates with salicylaldehyde derivatives over MgO and their transformation to the known coumarins is described. The satisfactory results were obtained with good yields, short reaction time, and simplicity in the experimental procedure. J. Heterocyclic Chem., (2009). [source] A facile route to the synthesis of 1,4-pyranonaphthoquinone derivatives under microwave irradiation without catalystJOURNAL OF HETEROCYCLIC CHEMISTRY, Issue 5 2009Xing-Han Wang A series of 1,4-pyranonaphthoquinone derivatives were synthesized via the reaction of arylidenemalononitrile and 2-hydroxynaphthalene-1,4-dione in the mixed solvent of N,N-dimethylformamide and glacial acetic acid (HOAc) under microwave irradiation without catalyst. This protocol has the notable advantages of short reaction time, high yield, and convenient operation. J. Heterocyclic Chem., (2009). [source] A facile and efficient synthesis of N -substituted furo[3,4- b]indeno[2,1- e]pyridine analogues of azapodophyllotoxin via microwave-assisted multicomponent reactionsJOURNAL OF HETEROCYCLIC CHEMISTRY, Issue 5 2009Feng Shi The efficient and facile synthesis of N -substituted furo[3,4- b]indeno[2,1- e]pyridine analogues of azapodophyllotoxin was achieved via microwave-assisted multicomponent reactions of aldehyde, 2H -indene-1,3-dione and 4-(arylamino)furan-2(5H)-one in glycol without catalyst. This method has the obvious advantages over traditional heating ones on short reaction time, high yield, operational simplicity as well as being environmental friendly. J. Heterocyclic Chem., (2009). [source] Microwave induced efficient synthesis of (un)substituted benzaldehyde (5-aryl-1,3,4-thiadiazol-2-yl)hydrazones using silica-supported dichlorophosphate as a recoverable dehydrantJOURNAL OF HETEROCYCLIC CHEMISTRY, Issue 5 2008Zheng Li (Un)substituted benzaldehyde (5-aryl-1,3,4-thiadiazol-2-yl)hydrazones were efficiently synthesized by reactions of (un)substituted benzaldehyde thiocarbohydrazones with aromatic carboxylic acids by using silica-supported dichlorophosphate as a recoverable dehydrant under microwave irradiation. The protocol has advantages of short reaction time, high yield, easy work-up procedure and no environmental pollution. [source] A new biginelli reaction procedure using potassium hydrogen sulfate as the promoter for an efficient synthesis of 3,4-dihydropyrimidin-2(1H)-oneJOURNAL OF HETEROCYCLIC CHEMISTRY, Issue 2 2004Shujiang Tu Simple and improved conditions have been found to carry out the Biginelli reaction for the synthesis of 3,4-dihydropyrimidin-2(1H)-one derivatives. This synthesis was performed using potassium hydrogen sulfate as the promoter in ethylene glycol solution. Compared with the classical Biginelli reaction conditions, this new method has the advantage of excellent yields (85,95%) and short reaction time (0.5,2 h). [source] Microwave-assisted TFA cleavage of peptides from Merrifield resinJOURNAL OF PEPTIDE SCIENCE, Issue 1 2010Alicja Kluczyk Abstract Microwave-assisted (MW) reactions are of special interest to the chemical community due to faster reaction times, cleaner reactions and higher product yields. The adaptation of MW to solid phase peptide synthesis resulted in spectacular syntheses of difficult peptides. In the case of Merrifield support, used frequently in synthesis of special peptides, the conditions used in product cleavage are not compatible with off-resin monitoring of the reaction progress. The application of MW irradiation in product removal from Merrifield resin using trifluoroacetic acid (TFA) was investigated using model tetrapeptides and the effects were compared with standard trifluoromethanesulphonic acid (TFMSA) cleavage using elemental analysis as well as chromatographic (HPLC) and spectroscopic (IR) methods. The deprotection of benzyloxycarbonyl and benzyl groups in synthetic bioactive peptides was analyzed using LC-MS and MS/MS experiments. In a 5 min microwave-assisted TFA reaction at low temperature, the majority of product is released from the resin, making the analytical scale MW-assisted procedure a method of choice in monitoring the reactions carried out on Merrifield resin due to the short reaction time and compatibility with HPLC and ESI-MS conditions. Copyright © 2009 European Peptide Society and John Wiley & Sons, Ltd. [source] A New Synthetic Method for the Preparation of Star-Shaped Polyisobutylene with Hyperbranched Polystyrene CoreMACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 13 2007Gergely Kali Abstract Friedel,Crafts self-grafting of polystyrene (PSt) under quasiliving carbocationic polymerization was utilized to develop a new rapid one-pot method for the preparation of star-shaped polyisobutylene (PIB). First, the polymerization of isobutylene led to PIB with predetermined molecular weight (,=,2,000) and narrow molecular weight distribution (,=,1.03). Then addition of relatively small amount of styrene after isobutylene consumption yielded PIB-PSt diblocks. Multiple alkylation of the resulting PSt segments by the polystyryl cations led to hyperbranched PSt cores coupling PIB chains to form a star polymer in short reaction time (within an hour) compared to reported methods. The formation of star polymers by this self-grafting mechanism was proved by gel permeation chromatography equipped with online viscosimeter and 1H NMR spectroscopy. [source] Organocatalytic synthesis of cyanohydrin trimethylsilyl ethers by potassium 4-benzylpiperidinedithiocarbamate under solvent-free conditionsAPPLIED ORGANOMETALLIC CHEMISTRY, Issue 3 2010Mohammad G. Dekamin Abstract Potassium 4-benzylpiperidinedithiocarbamate was found to be an efficient organocatalyst for facile addition of trimethylsilyl cyanide to a wide variety of aldehydes and ketones to afford corresponding cyanohydrin trimethylsilyl ethers in high to quantitative yields. The reaction proceeded smoothly by employing 2.0 mol% PBPDC loading under mild conditions at room temperature within a very short reaction time. Copyright © 2009 John Wiley & Sons, Ltd. [source] Multi-Component Synthesis of Dihydropyrimidines by Iodine Catalyst at Ambient Temperature and in-vitro Antimycobacterial ActivityARCHIV DER PHARMAZIE, Issue 8 2009Paresh Zalavadiya Abstract An efficient and simple three-component domino synthesis of some new dihydropyrimidines (DHPMs) from aromatic aldehydes, 1,3-dicarbonyl compounds and N -(3-chloro-4-fluorophenyl)urea using molecular iodine as catalyst is described. The 1-substituted dihydropyrimidines were isolated in good to excellent yields (78-90%) within a short reaction time (4-6 h) at ambient temperature. The biological evaluation revealed that the newly synthesized compounds (4a - i and 5a - i) exhibited moderate antimycobacterial activity against Mycobacterium tuberculosis H37 RV. [source] ChemInform Abstract: Synthesis of 3,4-Dihydropyrimidin-2(1H)-ones Using Ce(SO4)2,SiO2 as a Heterogeneous and Recyclable Catalyst.CHEMINFORM, Issue 40 2010Wen Pei Abstract Compared with the classical Biginelli reaction, the presented new method has the advantages of better product yields, short reaction time, easy separation and tolerance towards various functional groups. [source] Fast and Eco-friendly Synthesis of Dipyrromethanes by H2SO4·SiO2 Catalysis under Solvent-free ConditionsCHINESE JOURNAL OF CHEMISTRY, Issue 2 2010Yan Zhang Abstract For the first time, sillica-supported sulfuric acid has been used as a heterogeneous, reusable and efficient catalyst at room temperature to give the corresponding dipyrromethanes in a very short reaction time. The new reaction procedure is simple and solvent is not required. [source] Sulfamic Acid as a Green and Reusable Catalyst for the Preparation of , -EnaminonesCHINESE JOURNAL OF CHEMISTRY, Issue 7 2009Lei WANG Abstract Sulfamic acid can effectively catalyze the reaction of ( -diketones with arylamines to afford the , -enaminones. The present method offers several advantages, such as high yield, short reaction time, mild conditions, easy work-up and catalyst recyclability. [source] Heterogeneous Palladium Chloride Catalyzed Ligand-free Suzuki-Miyaura Coupling Reactions at Ambient TemperatureCHINESE JOURNAL OF CHEMISTRY, Issue 9 2008Min WANG Abstract A mild and efficient ligand-free Suzuki-Miyaura coupling reaction catalyzed by heterogeneous palladium chloride was developed at room temperature in a short reaction time under air atmosphere. Various phenyl iodides, bromides and activated chlorides were coupled with sodium tetraphenylborate or phenylboronic acids efficiently to afford the corresponding cross-coupled products in good to excellent yields. Furthermore, the catalyst could be recycled up to four times without loss of its activity. [source] Highly Efficient Pd/C-Catalyzed Suzuki Coupling Reaction of p -(un)Substituted Phenyl Halide with (p -Substituted phenyl) Boronic AcidCHINESE JOURNAL OF CHEMISTRY, Issue 8 2007Ming-Gang Hu Abstract A highly efficient Pd/C-catalyzed ligandless, heterogeneous Suzuki reaction of p -(un)substituted phenyl halide with (p -substituted phenyl)boronic acid in DMF/H2O solvent in a short reaction time (0.5 h) at 75 °C was developed. The key for such a catalytic system was the addition of 1 equivalent of tetrabutylammonium bromide. A wide variety of substituents can be tolerated and high yields of cross coupling products were achieved. The palladium catalyst can be easily recovered and reused without significantly decreasing its efficiency. [source] One-pot Synthesis of Bis(dihydropyrimidinone-4-yl)benzene Using Boric Acid as a CatalystCHINESE JOURNAL OF CHEMISTRY, Issue 5 2005Tu Shu-Jiang Abstract A simple effective synthesis of bis(dihydropyrimidinone-4-yl)benzene derivatives, using boric acid as catalyst, from isophthalic aldehyde or terephthalic aldehyde, 1,3-dicarbonyl compounds and urea or thiourea in glacial acetic acid was described. As the expansion of the classical Biginelli reaction, this method has the advantage of excellent yields 83%,94% and short reaction time 0.5,1.5 h. [source] Samarium-promoted Chemoselective Reduction of Aromatic Nitro Compounds in Ionic LiquidCHINESE JOURNAL OF CHEMISTRY, Issue 9 2002Xing-Liaiig Zheng Abstract The differently substituted aromatic nitro compounds were chemoselectively reduced by Sm/HOAc system in an ionic liquid medium to afford aromatic amines. Under these conditions the other substituents, such as -X, -CHO, -COOH, -CN, -NHTos and -alkyl, remained intact. The notable advantages of this reaction are its mild conditions, simple operation, short reaction time, high yields and easy recycling of ionic liquid. [source] Unsupported Copper Nanoparticles in the 1,3-Dipolar Cycloaddition of Terminal Alkynes and Azides,EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 10 2010Francisco Alonso Abstract Readily prepared copper nanoparticles were found to catalyse the 1,3-dipolar cycloaddition of azides and alkynes up to rates comparable to those of microwave chemistry. Both the preparation of the nanoparticles and the click reaction are carried out under mild conditions, in short reaction times and in the absence of any stabilising additive or ligand. A variety of 1,2,3-triazoles were prepared in excellent yields. A reaction mechanism was postulated on the basis of different reactivity studies and deuteration experiments. Copper(I) acetylides were demonstrated to be the real intermediate species. [source] Synthesis of ,-Amino Nitriles from Carbonyl Compounds, Amines, and Trimethylsilyl Cyanide: Comparison between Catalyst-Free Conditions and the Presence of Tin Ion-Exchanged MontmorilloniteEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 9 2010Jiacheng Wang Abstract In the absence of catalysts, the three-component, one-pot synthesis of ,-amino nitriles proceeded using various aldehydes and ketones together with amines and trimethylsilyl cyanide (TMSCN) in high yields under neat conditions at room temperature. The addition order of the reagents had a significant influence on the yields of the desired ,-amino nitriles. In contrast, when tin ion-exchanged montmorillonite (Sn-Mont), prepared by the ion-exchange of sodium montmorillonite (Na-Mont) with a tin tetrachloride solution, was used as a catalyst, the reaction rates significantly increased compared with those without catalysts, and the range of the applicable carbonyl compounds was also extended: structurally diverse aromatic, aliphatic and heteroatom-containing carbonyl compounds, including sterically hindered ketones as well as aliphatic and aromatic amines, were converted into the desired ,-amino nitriles in good to excellent yields with short reaction times under mild conditions. Sn-Mont showed a better catalytic activity than proton or other metal ion-exchanged montmorillonites, supported SnO2 catalysts and the previously reported homogeneous or heterogeneous catalysts. The recovered catalyst was reused several times without loss of catalytic performance. Along with the expansion of the interlayer space of Sn-Mont, the strong Brønsted acid and Lewis acid nature of Sn-Mont derived from protons and SnO2 nanoparticles present in the interlayers of Sn-Mont likely played important and cooperative roles in the high catalytic activity. [source] | ||||||||||||||||||||||||||||