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Isolated Yield (isolated + yield)
Kinds of Isolated Yield Selected AbstractsAn Efficient Route to Group 6 and 8 Metallaborane Compounds: Synthesis of arachno -[Cp*Fe(CO)B3H8] and closo -[(Cp*M)2B5H9] (M = Mo, W)EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 11 2009K. Geetharani Abstract Reaction of [Cp*Fe(CO)2I] (Cp* = ,5 -C5Me5) with an excess amount of BH3·thf in toluene at 75 °C or with LiBH4 at ,78 °C leads to the isolation of hydrogen-rich ferraborane arachno -[Cp*Fe(CO)B3H8] in good yield. In a similar fashion, reaction of [Cp*M(CO)3Cl] (M = Mo and W) with an excess amount of BH3·thf at 80 °C or at ,78 °C with LiBH4 yielded metallaboranes [(Cp*M)2B5H9] (M = Mo, W). Isolated yields of closo -[(Cp*M)2B5H9], (M = Mo and W), both from LiBH4 and BH3·thf, are good. All compounds were characterized in solution by IR, 1H, 11B, and 13C NMR spectroscopy and mass spectrometry and the structural types were unequivocallyestablished by crystallographic analysis of arachno -[Cp*Fe(CO)B3H8].(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) [source] Blocking Fluorine Substitution in Biotransformation of Nortricyclanyl N -Phenylcarbamates with Beauveria bassianaEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 11 2003Günter Haufe Abstract The biotransformation of tricyclo[2.2.1.02,6]hept-3-yl N -phenylcarbamate (8) by a standard procedure using Beauveria bassiana gave a 7:1 mixture of optically active exo,exo - and exo,endo -5-hydroxytricyclo[2.2.1.02,6]hept-3-yl N -phenylcarbamates 15 and 16 in 19% isolated yield. No ring opening of the three-membered ring was observed. Substitution with a fluorine atom at the 5- endo - or 5- exo -position prevented hydroxylation of any alicyclic position of the molecules, p -hydroxylation of the aromatic ring occurring to a small extent instead. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003) [source] Stereoselective Synthesis of Three Isomers of tert -Butyl 5-Hydroxy-4-methyl-3-oxohexanoate through Alcohol Dehydrogenase-Catalyzed Dynamic Kinetic ResolutionADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 1-2 2009Steffen Lüdeke Abstract Regioselective reduction of the 5-keto group of tert -butyl 4-methyl-3,5-dioxohexanoate (1) leads to a stereodiad of tert -butyl 5-hydroxy-4-methyl-3-oxohexanoate (2). Alcohol dehydrogenases from Lactobacillus brevis (LBADH), Rhodococcus sp. (RS 1-ADH) and Saccharomyces cerevisiae (YGL157w) reduce 1 under dynamic kinetic resolution conditions, thereby establishing two chiral carbons with a single reduction step. While it had been shown previously that LBADH reduction of 1 stereoselectively leads to syn -(4S,5R)- 2, alcohol dehydrogenase-mediated dynamic kinetic resolution now allows easy access to syn -(4R,5S)- 2 (RS 1-ADH; 97.6% ee, syn:anti=92:8, 66% conversion, 37% isolated yield) and anti -(4S,5S)- 2 (YGL157w; 90% ee, anti:syn=93:7, 64% conversion, 42% isolated yield), as well. Thus three out of four possible stereoisomers were formed selectively upon reduction of 1. [source] Enzyme-Catalyzed Synthesis of a Hybrid N-Linked Oligosaccharide using N-Acetylglucosaminyltransferase IADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 11-12 2008Rui Chen Abstract The soluble catalytic domain of human N-acetylglucosaminyltransferase I was purified from Escherichia coli and utilized in the enzyme-catalyzed conversion of high mannose N-linked oligosaccharide 1 into the rare hybrid oligosaccharide 2. Analysis of the reaction showed that the conversion of high mannose 1 into hybrid oligosaccharide 2 proceeded to 100% completion as assessed by MALDI-TOF-MS. Purification of the large polar oligosaccharide by gel filtration and silica gel chromatography afforded a 42% isolated yield of oligosaccharide 2. This enzyme-catalyzed reaction can be utilized to produce rare hybrid oligosaccharides for biochemical and structural studies. [source] An Efficient Bismuth(III) Chloride-Catalyzed Synthesis of 1,1-Diarylalkenes via Friedel,Crafts Reaction of Acyl Chloride or Vinyl Chloride with ArenesADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 14 2006Hongbin Sun Abstract In the presence of catalytic amount of bismuth(III) chloride, the reactions of acyl chlorides or vinyl chlorides with arenes afforded 1,1-diarylalkenes in 25,82,% isolated yield. In the case of the reaction of acyl chlorides with arenes, the procedure includes an initial Friedel,Crafts acylation, subsequent formation of vinyl chlorides and final Friedel,Crafts-type vinylation of another arene molecule with vinyl chloride. This paper reports the first Lewis acid-catalyzed cleavage of the CCl bond of vinyl chloride and its application in the synthesis of multiply subtituted alkenes. [source] Sodium Perborate,A Convenient Baeyer,Villiger Oxidation Reagent in the Synthesis of the Corey AldehydeADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 3 2003Maria Espiritu Abstract Sodium perborate tetrahydrate is a cheap, safe and readily available alternative to the commonly used peracetic acid for the Baeyer,Villiger oxidation step of the Corey aldehyde synthesis. Chloroketo acid 1 is smoothly converted by sodium perborate tetrahydrate in formic acid to the chloroketolactone 2 in 66% isolated yield. In contrast to previously reported reactions using other oxidants, the formation of the lactone is completely regioselective in favour of the "bridgehead-migrated" isomer 2. [source] Controlled vinyl-type polymerization of norbornene with a Nickel(II) diphosphinoamine/methylaluminoxane catalytic systemJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 20 2009Georgios C. Vougioukalakis Abstract A novel nickel-based complex coordinated with an asymmetric diphosphinoamine ligand was synthesized and fully characterized. Single crystals of good quality were also obtained, and the solid-state structure of the complex was studied via X-rays diffraction. The catalytic activity of this Ni(II) complex in the vinyl-type polymerization of norbornene was studied with methylaluminoxane (MAO) as the cocatalyst/activator. The influence of the reaction time, the equivalents of MAO used, and the concentration of the monomer on: (i) the activity of the catalytic system; (ii) the isolated yield of the polymer; and (iii) the molecular weight and molecular weight distribution of the polymer were investigated. The isolated polynorbornene (PNB) yields are significantly higher compared with those reported for other similar nickel-based systems. The as-obtained PNBs are characterized by high molecular weights and relatively narrow and monomodal molecular weight distributions (amongst the narrowest reported in the literature). The linear dependence of the molecular weight of the obtained PNB on the concentration of norbornene points toward a controlled polymerization reaction. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 5241,5250, 2009 [source] Synthesis and Properties of Novel Cross-Linked Fluoroalkyl End-Capped Oligomeric Nanoparticles Containing Adamantane UnitsMACROMOLECULAR RAPID COMMUNICATIONS, Issue 6 2007Masaki Mugisawa Abstract Fluoroalkyl end-capped cooligomers that contain both oxime-blocked isocyanato and hydroxyadamantyl segments are prepared by the cooligomerization of fluoroalkanoyl peroxide with the corresponding monomers under mild conditions. This fluorinated cooligomer affords new cross-linked fluoroalkyl end-capped cooligomeric nanoparticles that contain adamantane segments by the deprotecting reaction of oxime-blocked isocyanato segments in cooligomers in excellent to moderate isolated yield. A variety of cross-linked fluoroalkyl end-capped cooligomeric nanoparticles that contain adamantane segments are also prepared by similar deprotecting reactions with this fluorinated cooligomer in the presence of adamantane-1,5-diol. Furthermore, we have prepared cross-linked fluoroalkyl end-capped cooligomers that contain oxime-blocked isocyanato segments by the use of 2-hydroxyethyl acrylate and poly(ethylene glycol)-containing methacrylate monomer as comonomers, respectively. However, the deprotecting reactions of the oxime-blocked isocyanato segments in the cooligomers do not afford the expected nanoparticles, and these cross-linked cooligomers are found to show a gelling characteristic. The thermal stability of these cross-linked fluorinated cooligomeric nanoparticles that contain adamantane segments increases significantly compared to that of the parent fluorinated cooligomer. More interestingly, the thermal stability of these cross-linked fluorinated nanoparticles is almost the same as that of the fluoroalkyl end-capped acrylic acid oligomer/SiO2 nanocomposites (content of SiO2 in composites: 70%). In addition, these cross-linked fluorinated nanoparticles have been applied to the surface modification of traditional organic polymers such as poly(methyl methacrylate) to exhibit a good oleophobicity imparted by fluorine on their surface. [source] Copper-catalyzed asymmetric 1,4-conjugate addition of dialkylzinc to enonesAPPLIED ORGANOMETALLIC CHEMISTRY, Issue 7 2010Shaohua Gou Abstract Asymmetric 1,4-conjugation addition of dialkylzinc (diethylzinc and dimethylzinc) to cyclic enones, chalcone and nitroalkenes was achieved by a 25 mol% (R)-6,6,-Br2 -BINOL(1f), 25 mol% CuSPh and 100 mol% dicyclohexylmethylamin(Cy2NMe) catalyst system. The Cu(I) catalyst system enables the cyclic enone, chalcone and nitroalkene generality with high enantioselectivity (up to 84% ee) and isolated yield (up to 94%) under mild reaction conditions. Copyright © 2010 John Wiley & Sons, Ltd. [source] Improved synthesis of 5-hydroxylysine (Hyl) derivatives,CHEMICAL BIOLOGY & DRUG DESIGN, Issue 2 2005M. Cudic Abstract:, The synthesis of 5-hydroxylysine (Hyl) derivatives for incorporation by solid-phase methodologies presents numerous challenges. Hyl readily undergoes intramolecular lactone formation, and protected intermediates often have poor solubilities. The goals of this work were twofold: first, develop a convenient method for the synthesis of O -protected Fmoc-Hyl; secondly, evaluate the efficiency of methods for the synthesis of O -glycosylated Fmoc-Hyl. The 5- O - tert -butyldimethylsilyl (TBDMS) fluoren-9-ylmethoxycarbonyl-Hyl (Fmoc-Hyl) derivative was conveniently prepared by the addition of tert -butyldimethylsilyl trifluoromethanesulfonate to copper-complexed Hyl[, - tert -butyloxycarbonyl (Boc)]. The complex was decomposed with Na+ Chelex resin and the Fmoc group added to the , -amino group. Fmoc-Hyl(, -Boc, O -TBDMS) was obtained in 67% overall yield and successfully used for the solid-phase syntheses of 3 Hyl-containing peptides. The preparation of Fmoc-Hyl[, -Boc, O -(2,3,4,6-tetra- O -acetyl- , - d -galactopyranosyl)] was compared for the thioglycoside, trichloroacetimidate and Koenigs,Knorr methods. The most efficient approach was found to be Koenigs,Knorr under inverse conditions, where Fmoc-Hyl(, -Boc)-OBzl and peracetylated galactosyl bromide were added to silver trifluoromethanesulfonate in 1,2-dichloroethane, resulting in a 45% isolated yield. Side-reactions that occurred during previously described preparations of glycosylated Hyl derivatives, such as lactone formation, loss of side-chain protecting groups, orthoester formation, or production of anomeric mixtures, were avoided here. Research on the enzymology of Lys hydroxylation and subsequent glycosylation, as well as the role of glycosylated Hyl in receptor recognition, will be greatly aided by the convenient and efficient synthetic methods developed here. [source] [(NHC)(NHCewg)RuCl2(CHPh)] Complexes with Modified NHCewg Ligands for Efficient Ring-Closing Metathesis Leading to Tetrasubstituted Olefins,CHEMISTRY - A EUROPEAN JOURNAL, Issue 13 2010Volodymyr Sashuk Abstract Imidazolium salts (NHCewg,HCl) with electronically variable substituents in the 4,5-position (H,H or Cl,Cl or H,NO2 or CN,CN) and sterically variable substituents in the 1,3-position (Me,Me or Et,Et or iPr,iPr or Me,iPr) were synthesized and converted into the respective [AgI(NHC)ewg] complexes. The reactions of [(NHC)RuCl2(CHPh)(py)2] with the [AgI(NHCewg)] complexes provide the respective [(NHC)(NHCewg)RuCl2(CHPh)] complexes in excellent yields. The catalytic activity of such complexes in ring-closing metathesis (RCM) reactions leading to tetrasubstituted olefins was studied. To obtain quantitative substrate conversion, catalyst loadings of 0.2,0.5,mol,% at 80,°C in toluene are sufficient. The complex with the best catalytic activity in such RCM reactions and the fastest initiation rate has an NHCewg group with 1,3-Me,iPr and 4,5-Cl,Cl substituents and can be synthesized in 95,% isolated yield from the ruthenium precursor. To learn which one of the two NHC ligands acts as the leaving group in olefin metathesis reactions two complexes, [(FL-NHC)(NHCewg)RuCl2(CHPh)] and [(FL-NHCewg)(NHC)RuCl2(CHPh)], with a dansyl fluorophore (FL)-tagged electron-rich NHC ligand (FL-NHC) and an electron-deficient NHC ligand (FL-NHCewg) were prepared. The fluorescence of the dansyl fluorophore is quenched as long as it is in close vicinity to ruthenium, but increases strongly upon dissociation of the respective fluorophore-tagged ligand. In this manner, it was shown for ring-opening metathesis ploymerization (ROMP) reactions at room temperature that the NHCewg ligand normally acts as the leaving group, whereas the other NHC ligand remains ligated to ruthenium. [source] Co-Metal-Free Enantioselective Conjugate Addition Reactions of Zinc ReagentsCHEMISTRY - A EUROPEAN JOURNAL, Issue 36 2008Sefer Ay Dipl.-Chem. Abstract Asymmetric conjugate addition of diethylzinc to cinnamaldehyde in a co-metal-free fashion by using N,O-ligands with planar and central chirality is described. Different modulations of the ligand structure, including several combinations of the chiral units, indicate that a [2.2]paracyclophane backbone is essential for the activity and the enantioselectivity of the generated active catalyst. By using the optimized ligand, an isolated yield of 90,% was obtained with up to 99,%,ee. [source] Rearrangement of a (Dithiolato)platinum(II) Complex Formed by Reaction of Cyclic Disulfide 7,8-Dithiabicyclo[4.2.1]nona-2,4-diene with a Platinum(0) Complex: Oxidation of the Rearranged (Dithiolato)platinum(II) ComplexCHEMISTRY - A EUROPEAN JOURNAL, Issue 15 2007Akihiko Ishii Prof. Abstract Reaction of the title bicyclic disulfide 16 with [(Ph3P)2Pt(,2 -C2H4)] (2) yielded the corresponding (dithiolato)platinum(II) complex 17 by oxidative addition. The initial product 17 isomerized at room temperature in a [1,5]-sulfur rearrangement to give another (dithiolato)platinum(II) complex 18 in high isolated yield. Oxidation reactions of 18 with dimethyldioxirane (DMD) provided (sulfenato-thiolato)platinum(II) 23, (sulfinato-thiolato)platinum(II) 24, (sulfenato-sulfinato)platinum(II) 25, and (disulfinato)platinum(II) 26 complexes, the structures of which were elucidated by NMR spectroscopy and X-ray crystallography. The oxidation process took place regioselectively in the first step and chemoselectively in the second. The selectivities are discussed. [source] Palladium-Catalyzed Intramolecular Oxidative Alkylation of 4-Pentenyl ,-Dicarbonyl CompoundsCHEMISTRY - A EUROPEAN JOURNAL, Issue 24 2004Cong Liu Abstract Reaction of 8-nonene-2,4-dione with a catalytic amount of [PdCl2(CH3CN)2] (2; 5 mol,%) and a stoichiometric amount of CuCl2 (2.5 equiv) at room temperature for 3 h led to oxidative alkylation and formation of 2-acetyl-3-methyl-2-cyclohexenone in 80,% isolated yield. The oxidative alkylation of 4-pentenyl ,-diketones tolerated a number of terminal acyl groups and substitution at the C1 and C3 carbon atoms of the 4-pentenyl chain. Likewise, 4-pentenyl ,-keto esters that possessed geminal disubstitution at the C1, C2, or C3 carbon atom of the 4-pentenyl chain cyclized to form 2-carboalkoxy-2-cyclohexenones in moderate to good yield as the exclusive cyclized product. Deuterium-labeling experiments provided information regarding the mechanism of the palladium-catalyzed oxidative alkylation of 4-pentenyl ,-dicarbonyl compounds. [source] Catalytic Asymmetric Bromination and Chlorination of ,-KetoestersCHEMISTRY - A EUROPEAN JOURNAL, Issue 9 2004Mauro Marigo Abstract The first general catalytic asymmetric bromination and chlorination of ,-ketoesters has been developed. The reactions proceed for both acyclic and cyclic ,-ketoesters catalyzed by chiral bisoxazolinecopper(II) complexes giving the corresponding optically active ,-bromo- and ,-chloro-,-ketoesters in high yields and moderate to good enantioselectivities. For the optically active chlorinated products the isolated yields are in the range of 88,99,% and the enantiomeric excesses up to 77,% ee, while the optically active brominated adducts are formed in 70,99,% isolated yield and up to 82,% ee. Based on the absolute configuration of the optically active products, the face selectivity for the catalytic enantioselective halogenation is discussed based on a bidentate coordination of the ,-ketoester to the chiral catalyst and a X-ray structure of chiral ,,,-diketoesterenolatebisoxazolinecopper(II) complex. [source] Graphite-Supported Gold Nanoparticles as Efficient Catalyst for Aerobic Oxidation of Benzylic Amines to Imines and N -Substituted 1,2,3,4-Tetrahydroisoquinolines to Amides: Synthetic Applications and Mechanistic StudyCHEMISTRY - AN ASIAN JOURNAL, Issue 10 2009Man-Ho So Abstract Selective oxidation of amines using oxygen as terminal oxidant is an important area in green chemistry. In this work, we describe the use of graphite-supported gold nanoparticles (AuNPs/C) to catalyze aerobic oxidation of cyclic and acyclic benzylic amines to the corresponding imines with moderate-to-excellent substrate conversions (43,100,%) and product yields (66,99,%) (19,examples). Oxidation of N -substituted 1,2,3,4-tetrahydroisoquinolines in the presence of aqueous NaHCO3 solution gave the corresponding amides in good yields (83,93,%) with high selectivity (up to amide/enamide=93:4) (6,examples). The same protocol can be applied to the synthesis of benzimidazoles from the reaction of o -phenylenediamines with benzaldehydes under aerobic conditions (8,examples). By simple centrifugation, AuNPs/C can be recovered and reused for ten consecutive runs for the oxidation of dibenzylamine to N -benzylidene(phenyl)methanamine without significant loss of catalytic activity and selectivity. This protocol "AuNPs/C+O2" can be scaled to the gram scale, and 8.9,g (84,% isolated yield) of 3,4-dihydroisoquinoline can be obtained from the oxidation of 10,g 1,2,3,4-tetrahydroisoquinoline in a one-pot reaction. Based on the results of kinetic studies, radical traps experiment, and Hammett plot, a mechanism involving the hydrogen-transfer reaction from amine to metal and oxidation of M-H is proposed. [source] Highly Efficient Biomimetic Oxidation of Sulfide to Sulfone by Hydrogen Peroxide in the Presence of Manganese meso -TetraphenylporphyrinCHINESE JOURNAL OF CHEMISTRY, Issue 6 2008Xian-Tai ZHOU Abstract Low amount of manganese meso -tetraphenyl porphyrin [Mn(TPP)] was used for highly efficient selective oxidation of sulfide to sulfone by hydrogen peroxide at room temperature. Sulfones were produced directly with yields generally around 90% while the catalyst concentration was only 4×10,5 mol·L,1. In a large-scale experiment of thioanisole oxidation, the isolated yield of sulfone (87%) was obtained and the turnover number (TON) reached up to 8×106, which is the highest TON for the oxidation systems of sulfide to sulfone catalyzed by metalloporphyrins. [source] Iridium-Difluorphos-Catalyzed Asymmetric Hydrogenation of 2-Alkyl- and 2-Aryl-Substituted Quinoxalines: A General and Efficient Route into TetrahydroquinoxalinesADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 11-12 2010Damien Cartigny Abstract A highly efficient and general iridium-difluorphos-catalyzed asymmetric hydrogenation of diverse 2-alkyl- and 2-aryl-substituted quinoxalines into biologically and pharmaceutically relevant 2-substituted-1,2,3,4-tetrahydroquinoxaline units has been developed. High isolated yields and excellent enantioselectivities of up to 95% for 2-alkyl-substituted quinoxalines and of up to 94% for 2-aryl-substituted quinoxalines were obtained. [source] A Selective and Benign Synthesis of Functionalized Benzalacetones via Mizoroki,Heck Reaction Using Aryldiazonium SaltsADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 11-12 2010Therese Stern Abstract Palladium-catalyzed Mizoroki,Heck reactions were carried out in the presence of calcium carbonate in alcoholic solvents. Under these conditions an efficient preparation of functionalized benzalacetones was developed. The reactions were carried out at room temperature and aerobic conditions, giving the products within several minutes in up to 95% isolated yields. Furthermore, some kinetic investigations, mechanistic insights and considerations are presented. [source] Enantioselective Copper-Catalysed Allylic Alkylation of Cinnamyl Chlorides by Grignard Reagents using Chiral Phosphine-Phosphite LigandsADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 11-12 2010Wibke Lölsberg Abstract The copper(I)-catalysed SN2,-type allylic substitution of E -3-aryl-allyl chlorides (cinnamyl chlorides) using Grignard reagents represents a powerful method for the synthesis of compounds carrying a benzylic stereocentre. By screening a small library of modular chiral phosphine-phosphite ligands a new copper(I)-based catalyst system was identified which allows the performance of such reactions with exceptional high degrees of regio- and enantioselectivity. Best results were obtained using TADDOL-derived ligands (3,mol%), copper(I) bromide,dimethyl sulfide (CuBr,SMe2) (2.5,mol%) and methyl tert -butyl ether (MTBE) as a solvent. Various (1-alkyl-allyl)benzene derivatives were prepared with up to 99% ee (GC) in isolated yields of up to 99%. In most cases the product contained less than 3% of the linear regioisomer (except for ortho -substituted substrates). Both electron-rich and electron-deficient cinnamyl chlorides were successfully employed. The absolute configuration of the products was assigned by comparison of experimental and calculated CD spectra. The substrates were prepared from the corresponding alcohols by reaction with thionyl chloride. Initially formed mixtures of regioisomeric allylic chlorides were homogenised by treatment with CuBr,SMe2 (2.5,mol%) in the presence of triphenyl phosphine (PPh3) (3,mol%) in MTBE at low temperature to give the pure linear isomers. In reactions with methylmagnesium bromide (MeMgBr) an ortho -diphenylphosphanyl-arylphosphite ligand with an additional phenyl substituent in ortho, -position at the aryl backbone proved to be superior. In contrast, best results were obtained in the case of higher alkyl Grignard reagents (such as ethyl-, n -butyl-, isopropyl-, and 3-butenylmagnesium bromides) with a related ligand carrying an isopropyl substituent in ortho, -position. The method was tested on a multi-mmol scale and is suited for application in natural product synthesis. [source] Immobilization of Porphyrinatocopper Nanoparticles onto Activated Multi-Walled Carbon Nanotubes and a Study of its Catalytic Activity as an Efficient Heterogeneous Catalyst for a Click Approach to the Three-Component Synthesis of 1,2,3-Triazoles in WaterADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 14-15 2009Hashem Sharghi Abstract An efficient, regioselective, one-pot and two-step synthesis of ,-hydroxy 1,4-disubstituted 1,2,3-triazoles from a wide range of non-activated terminal alkynes and epoxides and sodium azide by way of a three-component click reaction using a catalytic amount of [meso -tetrakis(o -chlorophenyl)porphyrinato]copper(II) (5,mol%) in excellent isolated yields is described. The reactions were performed in water as a green solvent at ambient temperature without any additives. By performing two reaction steps in one pot and purifying only at the final step, this procedure excludes any interim purification of in situ generated organic azide intermediates, which significantly improves the overall yield and reduces the reaction time. To benefit from the recovery and reuse of the catalyst, a new heterogeneous catalyst was prepared by simple and successful impregnation of the catalyst onto activated multi-walled carbon nanotubes (AMWCNT). The heterogeneous catalyst was characterized by powder X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), atomic forced microscopy (AFM), and thermogravimetric (TG) analysis to estimate the amount of nitrogen adsorption, and Raman and FT-IR spectroscopy. Leaching experiments after ten successive cycles showed that the catalyst is most strongly anchored to the AMWCNT support. Mechanistically, porphyrinatocopper catalyzes each step of the reaction in different ways as a bifunctional catalyst including epoxide ring opening by azide delivery to epoxide, forming in situ generated 2-azido alcohols followed by activation of the CC triple bond of the starting terminal alkynes by forming a porphyrinatocopper-acetylide intermediate and thereby promoting the [3+2]-cycloaddition reaction as the key step to form the triazole framework. [source] First Heterogeneous Ligand- and Salt-Free Larock Indole SynthesisADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 13 2009Nelly Batail Abstract A new ligand- and salt-free procedure using heterogeneous palladium catalysts for the Larock indole and benzofuran synthesis is reported. After optimisation of the reaction conditions, good to high isolated yields have been achieved for a variety of structures. Recycling studies have shown that the palladium catalysts can be readily recovered and reused. Reactions and recovery of the palladium catalysts can be carried out in the presence of air, without any particular precaution. [source] Convenient General Asymmetric Synthesis of Roche Ester Derivatives through Catalytic Asymmetric Hydrogenation: Steric and Electronic Effects of LigandsADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 16 2008Cyrielle Pautigny Abstract An efficient and concise asymmetric hydrogenation of acrylate esters promoted by the cationic ruthenium monohydride complex [Ru(H)(,6 -cot)SYNPHOS]+BF4, is reported. A full investigation of the effects of catalyst precursors, solvents, temperature, hydrogen pressure, substrates as well as steric and electronic properties of ligands was carried out. The corresponding valuable Roche ester derivatives were obtained in good to excellent isolated yields and high enantioselectivities under mild conditions. The robustness and practicability of this highly enantioselective hydrogenation was demonstrated by the synthesis of the 3-hydroxy-2-methylpropanoic acid tert -butyl ester on a multigram scale, resulting in excellent yield and ee up to 94%. [source] Enhanced Cooperativity in Hydrolytic Kinetic Resolution of Epoxides using Poly(styrene) Resin-Supported Dendronized Co-(Salen) CatalystsADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 11-12 2008Poorva Goyal Abstract Excellent enantioselectivities and isolated yields have been achieved for the hydrolytic kinetic resolution of epoxides using a resin-supported dendronized R,R-(salen)Co catalyst with catalyst loadings as low as 0.04 mol%, the lowest metal loadings of any heterogeneous resin-supported (salen)Co catalyst reported to date. In addition, the supported catalysts can be recycled and reused with comparable enantioselectivities. It is hypothesized that the high catalytic activity can be attributed to the flexible linker and the dendronized framework supporting the (salen)Co moieties on the resin thereby promoting cooperativity between two metal centers. This work opens up new opportunities for the design of highly active resin-supported catalysts that catalyze transformations through a bimetallic pathway. [source] Metal-Free, Enantioselective Strecker Reactions Catalyzed by Chiral BINOL and TADDOL CatalystsADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 4-5 2007Magnus Rueping Abstract An efficient, metal-free Brønsted acid-catalyzed, enantioselective hydrocyanation of ketoimines has been developed. This BINOL phosphate-catalyzed Strecker reaction provides the corresponding amino nitriles, precursors of quaternary amino acids, in good isolated yields and enantioselectivities. Additionally, we demonstrate that chiral diols, such as TADDOL, are effective enantioselective catalysts for the hydrogen-bond activation of aldimines. [source] Asymmetric Cyanoethoxycarbonylation of Aldehydes Catalyzed by Heterobimetallic Aluminum Lithium Bis(binaphthoxide) and CinchonineADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 3 2007Shaohua Gou Abstract Highly efficient catalytic asymmetric cyanoethoxycarbonylation of aldehydes was achieved by 10 mol,% cinchonine with 10 mol,% heterometallic (S)-aluminum lithium bis(binaphthoxide), which gave the cyanohydrins ethyl carbonates in excellent isolated yields (up to 99,%) with moderate to high enantioselectivities (up to 95,% ee) under mild conditions (at ,20,°C). Especially, the solid aluminum lithium bis(binaphthoxide) free of tetrahydrofuran was obtained by a new procedure using (S)-bi(2-naphthol), aluminum isopropoxide and n -butyllithium in dichloromethane, which was insensitive to air and moisture and was very convenient to store and use. A catalytic cycle based on experimental phenomena was proposed to explain the nature of the asymmetric induction. [source] Novel fluorescent (p -phenylene ethynylene)-calix[4]arene-based polymer: Design, synthesis, and propertiesJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 19 2008Alexandra I. Costa Abstract A novel fluorescent (p -phenylene ethynylene)-calix[4]arene-based polymer (CALIX-PPE) has been successfully synthesized by cross-coupling polymerization of bis-calix[4]arene 1 with 1,4-diethynylbenzene. The polycondensation was carried out in toluene/NEt3 at 35 °C for 24 h, using PdCl2(PPh3)2/CuI as the catalytic system, furnishing CALIX-PPE in excellent isolated yields (higher than 95%, several runs). The yellow polymer is freely soluble in several nonprotic organic solvents. The GPC trace of the isolated polymer showed a monomodal distribution and a number-average molecular weight of 23,300 g mol,1 (Mw/Mn = 2.05). No evidence was found in the structural analysis (FTIR and 1H/13C NMR) regarding the formation of alkyne homocoupled segments along the polymer chain. For comparative purposes, the synthesis of an analogous poly(p -phenylene ethynylene) containing p - t -butyl-phenoxymethyl side chains (TBP-PPE) was also undertaken. A great similarity was found between the photophysical properties of CALIX-PPE and TBP-PPE in solution (UV,vis and laser induced luminescence), clearly demonstrating their unique dependence on the structure and conformation of the conjugated PPE backbone. The fluorescence spectra of polymers are of nearly identical shape, displaying their maximum emission around 420 nm. The calculated solution photoluminescence quantum yields of CALIX-PPE and TBP-PPE are of similar magnitude (,F(CALIX-PPE) = 0.43; ,F(TBP-PPE) = 0.51). © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 6477,6488, 2008 [source] Enantioselective alkynylation of aldehydes catalyzed by a camphor sulfonylated amino alcohols titanium(IV) catalyst systemAPPLIED ORGANOMETALLIC CHEMISTRY, Issue 5 2010Shaohua Gou Abstract A new titanium(IV) complex has been developed for the effective enantioselective alkynylation of phenylacetylene addition to aldehydes. The titanium(IV) complex was readily prepared in situ from (R)-C-(7,7-dimethyl-2-oxo-bicyclo[2.2.1]hept-1-yl)-(1R,2S)- N -(2-hydroxy-1,2-diphenyl-ethyl)-methanesulfonamide (1h) and tetraisopropyl titanate [Ti(i -OPr)4]. A variety of aromatic aldehydes and ,,,-unsaturated aldehydes were found to be suitable substrates in the presence of the camphor sulfonylated amino alcohol titanium(IV) complex [10 mol% 1h, 40 mol% Ti(i -OPr)4]. The desired propargylic alcohols were afforded with high isolated yields (up to 90%) and moderate enantioselectivities (up to 65% ee) under mild conditions. Copyright © 2010 John Wiley & Sons, Ltd. [source] Asymmetric 1,4-conjugation addition of diethylzinc to cyclic enones catalyzed by a self-assembled copper complexAPPLIED ORGANOMETALLIC CHEMISTRY, Issue 12 2009Shaohua Gou Abstract A new self-assembled catalyst system based on copper complex was developed for the 1,4-conjugation addition of diethyl zinc to cyclic enones. The self-assembled catalyst was readily prepared from (R)-[1,1,]binaphthalenyl-2,2,-diamine (1a), (L)-tryptophan (3f) and copper(I) chloride (CuCl). Several enones were found to be suitable substrates in the presence of the self-assembled copper catalyst [10 mol% (R)-1a, 10 mol% (L)-3f and 10 mol% CuCl] under optimized conditions. The desired products were afforded with high isolated yields (up to 98%) and moderate to good enantioselectivities (up to 80% ee) in mild conditions (at 0 °C). Copyright © 2009 John Wiley & Sons, Ltd. [source] ChemInform Abstract: anti-Diastereo- and Enantioselective Carbonyl (Hydroxymethyl)allylation from the Alcohol or Aldehyde Oxidation Level: Allyl Carbonates as Allylmetal Surrogates.CHEMINFORM, Issue 32 2010Yong Jian Zhang Abstract The first enantioselective carbonyl (hydroxymethyl)allylation in the presence of aromatic, allylic, or aliphatic alcohols (II) is reported employing an (S)-SEGPHOS-modified iridium C,O-benzoate complex to provide products (III) in good isolated yields, good anti-diastereoselectivities and high enantioselectivities. [source] | |||||||||||||||||||||||||