- Folding-driven reversible polymerization of oligo(m-phenylene ethynylene) imines: Solvent and starter sequence studies
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Bis(imino) end-functionalized oligo(m-phenylene ethynylene)s were equilibrated in a closed system under conditions that promote reversible imine metathesis. The metathesis reaction joins two oligomers and produces a small molecule byproduct. In polar solvents, equilibration gave high molecular weight polymers while equilibration in chloroform produced only low molecular weight oligomers. This polymerization is hypothesized to be driven by the free energy gained from the folding of the long polymer chains directed by the noncovalent, intramolecular aromatic stacking and solvophobic interactions. This polymerization was also conducted in a series of solvents in which m-phenylene ethynylene oligomers have previously shown varied, intermediate folding stabilities. These experiments revealed a good correlation of the product molecular weight with the stability of the m-phenylene ethynylene helix. The equilibrium state of the metathesis reaction was also demonstrated to depend on the chain length of the starter sequences. With a pair of trimeric precursors, macrocyclization instead of polymerization takes place. Consistent with the notion that the polymerization is a consequence of the intramolecular solvophobic chain association, higher degrees of polymerization followed from enhanced solvophobicity of the m-phenylene ethynylene backbone, achieved by appending a methyl substituent to half of the repeat units. The considerably longer equilibration time required by these more stabilized sequences suggests that the elongation process may involve unfolding or partial unfolding of the chain; alternatively, intermolecular association may be responsible for the slow chain growth.
- Zhao, Dahui,Moore, Jeffrey S.
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- A novel water-dispersible and magnetically recyclable nickel nanoparticles for the one-pot reduction-Schiff base condensation of nitroarenes in pure water
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In this work, a heterogeneous nanocatalyst called Ni-Fe3O4@Pectin~PPA ~ Piconal was first synthesized, which was investigated as a bifunctional catalyst containing nickel functional groups. On the other hand, this Ni-Fe3O4@Pectin~PPA ~ Piconal catalyst in aqueous solvents shows a very effective performance at ambient temperature for the nitroarene reduction reaction with sodium borohydride, for which NaBH4 is considered as a reducing agent. This is a novelty magnetic catalyst that was approved by various methods, including Fourier-transform infrared spectroscopy (FT-IR), X-ray powder diffraction (XRD), Dynamic light scattering (DLS), Transmission electron microscopy (TEM), vibrating sample magnetometer (VSM), Inductively coupled plasma (ICP), Energy-dispersive X-ray spectroscopy (EDX), and Field emission scanning electron microscopy (FESEM) analyses. From the satisfactory results obtained from the reduction of nitrogen, this catalytic system is used for a one-pot protocol containing a reduction-Schiff base concentration of diverse nitroarenes. It was corroborated with the heterogeneous catalytic experiments on the one-pot tandem synthesis of imines from nitroarenes and aldehydes. Finally, the novel Ni-Fe3O4@Pectin~PPA ~ Piconal catalyst could function as a more economically desirable and environmentally amicable in the catalysis field. The favorable products are acquired in good to high performance in the attendance of Ni-Fe3O4@Pectin~PPA ~ Piconal as a bifunctional catalyst. This catalyst can be recycled up to six steps without losing a sharp drop.
- Ghamari Kargar, Pouya,Ravanjamjah, Asiye,Bagherzade, Ghodsieh
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p. 1916 - 1933
(2021/07/10)
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- Ruthenium N-Heterocyclic Carbene Complexes for Chemoselective Reduction of Imines and Reductive Amination of Aldehydes and Ketones
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Chemoselective reduction of imines to secondary amines is catalyzed efficiently by tethered and untethered, half-sandwich ruthenium N-heterocyclic carbene (NHC) complexes at room temperature. The untethered Ru-NHC complexes are more efficient as catalysts for the reduction of aldimines and ketimines than the tethered complexes. Using the best untethered complex as a catalyst, electronic and steric demands on the reaction was probed using a series of imines. Chemoselectivity of the catalyst towards imine reduction was tested by performing inter and intramolecular competitive reactions in a variety of ways. The catalyst exhibits a very high TON and TOF under anaerobic conditions.
- Kathuria, Lakshay,Samuelson, Ashoka G.
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supporting information
(2020/06/17)
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- Improving C=N bond reductions with (Cyclopentadienone)iron complexes: Scope and limitations
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Herein, we broaden the application scope of (cyclo-pentadienone)iron complexes 1 in C=N bond reduction. The catalytic scope of pre-catalyst 1b, which is more active than the “Kn?lker complex” (1a) and other members of its family, has been expanded to the catalytic transfer hydrogenation (CTH) of a wider range of aldimines and ketimines, either pre-isolated or generated in situ. The kinetics of 1b-promoted CTH of ketimine S1 were assessed, showing a pseudo-first order profile, with TOF = 6.07 h–1 at 50 % conversion. Moreover, the chiral complex 1c and its analog 1d were employed in the enantioselective reduction of ketimines and reductive amination of ketones, giving fair to good yields and moderate enantioselectivity.
- Cettolin, Mattia,Bai, Xishan,Lübken, Dennis,Gatti, Marco,Facchini, Sofia Vailati,Piarulli, Umberto,Pignataro, Luca,Gennari, Cesare
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supporting information
p. 647 - 654
(2018/10/24)
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- Effects of molecular conformation on the spectroscopic properties of 4,4′-disubstituted benzylideneanilines
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The relationship between the molecular conformation and spectroscopic properties of unsymmetrical 4,4′-disubstituted benzylideneanilines, was explored by the combination of experiment and reference data. Crystal structure information and spectroscopic beh
- Fang, Zhengjun,Wu, Feng,Yi, Bing,Cao, Chenzhong,Xie, Xin
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- Oxazolidine synthesis by complementary stereospecific and stereoconvergent methods
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Complementary stereospecific and stereoconvergent reactions for enantioselective synthesis of 1,3-oxazolidines are reported. In the presence of a rhodium catalyst, reaction of enantioenriched butadiene monoxide with aryl imines is stereospecific (99% ee). Alternatively, the reaction of racemic butadiene monoxide, in the presence of a chiral palladium or nickel catalyst, provides an enantioselective synthesis of 1,3-oxazolidines (up to 94% ee). Synthesis of either the cis- or trans-1,3-oxazolidines is also accomplished under catalyst control.
- Shaghafi, Michael B.,Grote, Robin E.,Jarvo, Elizabeth R.
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supporting information; experimental part
p. 5188 - 5191
(2011/12/15)
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- Palladium-catalyzed, one-pot, three-component synthesis of homoallylic amines from aldehydes, anisidine, and allyl trifluoroacetate
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(Chemical Equation Presented) An allylation reaction that generates homoallylic amines using allyl trifluoroacetate as a nucleophilic allylmetal precursor is reported. A palladium complex catalyzes two transformations in one pot: formation of allylsilane
- Grote, Robin E.,Jarvo, Elizabeth R.
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supporting information; experimental part
p. 485 - 488
(2009/07/18)
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- Novel oxazabicycles as a new class of photochromic colorants
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(Chemical Equation Presented) A new photochromic colorant with an oxazabicyclic moiety has been synthesized by an efficient method. It turns pale red upon UV irradiation and undergoes reverse reaction while being heated. This work may open an exciting new
- Yang, Ding-Yah,Chen, You-Sheng,Kuo, Pei-Yu,Lai, Jiun-Ting,Jiang, Chang-Ming,Lai, Chin-Hung,Liao, Yong-Hong,Chou, Pi-Tai
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p. 5287 - 5290
(2008/09/17)
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- Pot, atom and step economic (PASE) synthesis of highly functionalized piperidines: a five-component condensation
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The diastereoselective pot, atom and step economic (PASE) synthesis of highly functionalized piperidines has been realized. The procedure simply involves mixing methyl acetoacetate, 2 equiv of aldehyde and 2 equiv of aniline together in the presence of InCl3. In most cases the piperidine precipitates out of solution.
- Clarke, Paul A.,Zaytzev, Andrey V.,Whitwood, Adrian C.
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p. 5209 - 5212
(2008/02/08)
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- Synthesis and characterization of coumarin and dimedone-derived diazabicycles
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A series of diazabicyclic derivatives were prepared in three to four steps from p-anisidine and p-nitrobenzaldehyde. The key step of the synthesis involved the acid-catalyzed coupling of 4-aminocoumarin or dimedone derivatives with amino alcohols 3 or 7 t
- Lai, Jiun-Ting,Kuo, Pei-Yu,Gau, Yung-Her,Yang, Ding-Yah
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p. 7796 - 7800
(2008/03/11)
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- Synthesis and characterization of [1]benzopyrano[4,3-d][1,3]benzooxazocin- 13-one and its derivatives
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This work describes the efficient synthesis of functionalized cleft molecules 6, 6a, 16, 16a, 17, 19 and 20 derived from benzopyrano[4,3-d][1,3] benzooxazocin-13-one. X-ray crystal structure analysis of compounds 6a and 16a revealed that the cleft angles of the planes of the benzopyran moiety and the p-methoxybenzene ring are 109.4° and 108.6°, respectively. The conformation of the aromatic ring at the bridgehead of 16, 16a and 20 is restricted by the gem-dimethyl groups on the C-9 position and the methyl group on the nitrogen atom in the ring. Georg Thieme Verlag Stuttgart.
- Wang, Jen-Fei,Liao, Yuan-Xiu,Kuo, Pei-Yu,Gau, Yung-Her,Yang, Ding-Yah
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p. 2791 - 2794
(2008/02/11)
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- Infrared irradiation: Effective promoter in the formation of N-benzylideneanilines in the absence of solvent
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Infrared irradiation promoted the formation of a series of Schiff bases in the condensation reaction between benzaldehydes and anilines, in the absence of solvent. Benzaldehydes and anilines, containing either electron-withdrawing or electron-releasing groups, were assessed to identify any substituent effect on the formation of the Schiff bases. This methodology is characterized by ease of set-up and work-up, and the reaction yields were comparable with those obtained in the methods reported previously. Moreover, this new procedure is environmentally benign because no solvent was employed in the transformations.
- Vazquez, Miguel A.,Landa, Miguel,Reyes, Leonor,Miranda, Rene,Tamariz, Joaquin,Delgado, Francisco
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p. 2705 - 2718
(2007/10/03)
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- Torsional vibration and central bond length of N-benzylideneanilines
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The crystal structures of N-benzylideneaniline (1), N-benzylidene-4- carboxyaniline (2), N-(4-methylbenzylidene)-4-nitroaniline (3), N-(4-nitrobenzylidene)-4-methoxyaniline (4), N-(4-nitrobenzylidene)-4- methylaniline (5), W-(4-methoxybenzylidene)aniline (6) and N-(4- methoxybenzylidene)-4-methylaniline (7) were determined by X-ray diffraction analyses at various temperatures. In the crystal structures of all the compounds, an apparent shortening of the central C=N bond was observed at room temperature. As the temperature was lowered, the observed bond lengths increased to approximately 1.28 A at 90 K, irrespective of substituents in the molecules. The shortening and the temperature dependence of the C=N bond length are interpreted in terms of an artifact caused by the torsional vibration of the C - Ph and N - Ph bonds in the crystals. In the crystal structures of (1) and (7), a static disorder around the C=N bond was observed, which is also responsible for the apparent shortening of the C=N bond.
- Harada, Jun,Harakawa, Mayuko,Ogawa, Keiichiro
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p. 578 - 588
(2007/10/03)
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- Modeling substituent-dependence of the twist and shielding in a series of 4-substituted N-(4-nitrobenzylidene)anilines
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A series of 15 4-substituted N-(4-nitrobenzylidene)anilines was synthesized and studied by 1H NMR spectroscopy. Their ab initio calculated geometries and the shielding as expressed by aromatic ring currents were used in correlation analysis. The geometries were fully optimized using density functional theory B3LYP/6-311G** approaches. For the determination of the ring current contribution to the shielding of azomethine hydrogens H α was used direct ab initio calculation of the chemical shielding in a model system. Experimental chemical shift values free of these contributions were successfully correlated with increments ap of chemical shift for monosubstituted benzenes. In the same manner, the contribution of the anisotropy of C=N double bond to Hm hydrogen were calculated and values of the Hm chemical shift free of this contribution were successfully correlated with increments of chemical shift am.
- Proks, Vladimir,Holik, Miroslav
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p. 1566 - 1576
(2007/10/03)
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- On the additions of lithium methyl p-tolyl sulfoxide to N-(PMP)arylaldimines
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The results presented in this paper confirm that the stereochemical outcome of the reversible additions of lithium (R)-methyl p-tolyl sulfoxide to N-arylidene-p-anisidines (N-PMP imines) depends on: (a) the reaction conditions used and (b) the electronic properties of the arylidene moiety on the starting imine. In particular, we show that under kinetic control (-70 °C) the additions involving electron-rich N-arylidene groups occur with very high stereocontrol in favor of the (2S,RS)-diastereomers, whereas an electron-deficient group favors the opposite stereochemical outcome. Based on the observations above, a mechanistic hypothesis is proposed.
- Zucca, Cristina,Bravo, Pierfrancesco,Corradi, Eleonora,Meille, Stefano V.,Volonterio, Alessandro,Zanda, Matteo
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p. 424 - 432
(2007/10/03)
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- Synthesis and antimicrobial activity of 1,4-diaryl-2-azetidinones
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Cycloaddition of substituted 4,4-benzylidene-anilines to in situ prepared dichloroketenes in the presence of dichloroacetyl chloride and triethylamine affords a variety of 2-azetidinones. All the compounds were characterized by IR and 1H NMR. Their antimicrobial activity, against Gram(+) and Gram(-) bacteria and fungi, was tested. Copyright (C) 2000 Elsevier Science S.A.
- Guener, Vildan,Yildirir, Sueleyman,Oezcelik, Berrin,Abbasoglu, Ufuk
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p. 147 - 150
(2007/10/03)
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- Mechanism of Thermal Z/E Isomerization of Substituted N-Benzylideneanilines. Nature of the Activated Complex with an sp-Hybridized Nitrogen Atom
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In order to study the mechanism of thermal geometrical isomerization involving a sp2-hybridized nitrogen atom, kinetic effects of substituent, solvent, and pressure were studied in substituted N-benzylideneanilines.The effect of the substituent on the aniline moiety was almost independent of the electronic nature of the benzylidene group, and the results could be described satisfactorily by log (k/k0) = ρ0 + r+(?+ - ?0) + r-(?- - ?0)>, except for the 4-(dimethylamino) group.The r- values were more than twice as large as r0, suggesting strongly that the aniline ring is in conjugation not with the carbon-nitrogen ? bond but with the nitrogen lone pair in the transition state.The lower activation enthalpies and fairly large negative activation entropies observed in N-(4-X-benzylidene)-4-nitroanilines also support this view.When a dimethylamino group exists in the 4-position of the aniline ring, the rate constants observed were larger than that expected from the above equation.This deviation suggests the existence of a reaction route where the two phenyl groups become coplanar in the transition state.Ab initio calculations on selected N-phenylformaldimines and N- benzylideneanilines were performed to characterize the actual relation between both reaction possibilities as alternative and parallel routes, respectively.On the basis of the experimental data, the rate constants for the two inversion isomerizations were estimated by assuming parallel reactions for three cases.
- Asano, Tsutomu,Furuta, Hiroyuki,Hofmann, Hans-Joerg,Cimiraglia, Renzo,Tsuno, Yuho,Fujio, Mizue
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p. 4418 - 4423
(2007/10/02)
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