- Iron(II)-Catalyzed Aerobic Biomimetic Oxidation of Amines using a Hybrid Hydroquinone/Cobalt Catalyst as Electron Transfer Mediator
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Herein we report the first FeII-catalyzed aerobic biomimetic oxidation of amines. This oxidation reaction involves several electron transfer steps and is inspired by biological oxidation in the respiratory chain. The electron transfer from the amine to molecular oxygen is aided by two coupled catalytic redox systems, which lower the energy barrier and improve the selectivity of the oxidation reaction. An iron hydrogen transfer complex was utilized as the substrate-selective dehydrogenation catalyst along with a bifunctional hydroquinone/cobalt Schiff base complex as a hybrid electron transfer mediator. Various primary and secondary amines were oxidized in air to their corresponding aldimines or ketimines in good to excellent yield.
- Guemundsson, Arnar,Manna, Srimanta,B?ckvall, Jan-E.
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supporting information
p. 11819 - 11823
(2021/04/29)
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- Nickel Complexes Bearing N,N,O-Tridentate Salicylaldiminato Ligand: Efficient Catalysts for Imines Formation via Dehydrogenative Coupling of Primary Alcohols with Amines
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Treatment of salicylaldiminato ligand L1H-L2H (L1H = 2,4-di-tert-butyl-6-((quinolin-8-ylimino)methyl)phenol; L2H = 2,4-di-tert-butyl-6-(((2-(diethylamino)ethyl)imino)methyl)phenol) with Ni(OAc)2·4H2O in refluxing ethanol afforded nickel complexes [(L1)Ni(OAc)] (1) and [(L2)Ni(OAc)] (2), respectively. Reaction of L3H (L3H = (2,4-di-tert-butyl-6-(((2-(pyridin-2-yl)ethyl)imino)methyl)phenol)) with Ni(OAc)2·4H2O in the presence of excess triethylanmine gave the dual ligands coordinated nickel complex [(L2)2Ni] (3). Complexes 1-3 were well characterized by high-resolution mass spectrometry, infrared spectroscopy, elemental analysis, and X-ray diffraction analysis. All the three Ni(II) complexes exhibited efficient activity and good selectivity in the acceptorless dehydrogenative coupling of alcohols and amines to produce imines and diimines. The present protocol provides an atom-economical and sustainable route for the synthesis of various imine derivatives by employing an earth-abundant nickel salt and easily prepared salicylaldiminato ligands.
- Han, Zhangang,Hao, Zhiqiang,Lin, Jin,Lu, Guo-Liang,Zhang, Junhua,Zhang, Xiaoying
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p. 3843 - 3853
(2021/11/18)
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- Cooperative catalysis of molybdenum with organocatalysts for distribution of products between amines and imines
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Multi-amino groups and nitrogen donors compound was discovered as an organocatalyst for N-alkylation of alcohols with amines in the presence of Mo(CO)6. The Mo(CO)6/organocatalyst binary system has shown to be a highly active catalyst for the N-alkylation reaction between alcohols and amines with excellent tolerance of variable starting materials bearing different functional groups. Of particular note, this method possessing a superiority selectivity in the synthesis of N-alkylated amines or imines, which can be controlled by the reaction temperature. The cooperative catalysis mechanism in combination of Mo(CO)6 with organocatalyst was elucidated by control experiments.
- Wu, Di,Bu, Qingqing,Guo, Cheng,Dai, Bin,Liu, Ning
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- Gold-Catalyzed Bicyclic and [3+2]-Annulations of Internal Propargyl Alcohols with Nitrones and Imines To Yield to Two Distinct Heterocycles
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A gold-catalyzed synthesis of 1,3-dihydrooxazolo[3,4-a]indoles from 1-oxo-3-yn-4-ols and nitrones is described; this new bicyclic annulation presents the first examples that internal alkynes can react with nitrones to undergo an oxoarylation route. DFT calculations indicate a [3,3]-sigmatropic shift of initial alkenylgold intermediates to elude the intermediacy of gold carbenes. We also developed new [3+2]-annulations of the same 1-oxo-3-yn-4-ols with imines, yielding oxazolidin-4-ylidene derivatives efficiently. The tethered alcohols of these 1-oxo-3-ynes allow trapping of their metastable 2-azadienium intermediates to enable a novel annulation. Our mechanistic analysis indicates that the two products, despite their structural relevance, are produced from two independent systems. (Figure presented.).
- More, Sayaji Arjun,Chao, Tzu-Hsuan,Cheng, Mu-Jeng,Liu, Rai-Shung
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supporting information
p. 525 - 531
(2020/12/01)
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- Inverse Hydroboration of Imines with NHC-Boranes Is Promoted by Diphenyl Disulfide and Visible Light
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We describe a simple and efficient procedure for nucleophilic borylation of imines in the absence of a photoredox catalyst. Visible light irradiation of an acetonitrile solution of an imine, an NHC-borane, and diphenyl disulfide (10 mol %) provides various stable α-amino NHC-boranes in good yields. The reaction proceeds via addition of a nucleophilic boryl radical to an imine, followed by hydrogen abstraction from thiophenol, which is generated from NHC-borane and diphenyl disulfide.
- Kawamoto, Takuji,Morioka, Tsubasa,Noguchi, Kohki,Curran, Dennis P.,Kamimura, Akio
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supporting information
p. 1825 - 1828
(2021/03/08)
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- Synthesis of chromeno[3,4-b]piperazines by an enol-ugi/reduction/cyclization sequence
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Keto piperazines and aminocoumarins are privileged building blocks for the construction of geometrically constrained peptides and therefore valuable structures in drug discovery. Combining these two heterocycles provides unique rigid polycyclic peptidomimetics with drug-like properties including many points of diversity that could be modulated to interact with different biological receptors. This work describes an efficient multicomponent approach to condensed chromenopiperazines based on the novel enol-Ugi reaction. Importantly, this strategy involves the first reported post-condensation transformation of an enol-Ugi adduct.
- Bornadiego, Ana,Neo, Ana G.,Marcos, Carlos F.
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supporting information
(2021/05/31)
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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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- Insight into the Modes of Activation of Pyridinium and Bipyridinium Salts in Non-Covalent Organocatalysis
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A series of pyridinium and bipyridinium salts were prepared and their catalytic properties were evaluated in the aza-Diels-Alder reaction between imines and Danishefsky diene. Depending on the substituents of the pyridinium/bipyridinium rings and on the nature of the counterion, two mechanisms of activation were demonstrated. In case of non-substituted rings, the substrate is activated through charge transfer involving the aryl ring on the C-side of the imine. When halogen atoms were introduced on the catalysts, the activation mode switched to halogen bond involving the imine nitrogen lone pair. Moreover, alternative activation modes based on hydrogen bonding and radical cation were ruled out. This work allowed us to develop two families of catalysts whose potential was demonstrated in the cycloaddition of various imines with Danishefsky diene. The first family is composed of the simple methyl pyridinium triflate and dioctyl bipyridinium triflate. The former is active only with imines bearing a p-methoxyphenyl group on the C-side and the latter was found to be efficient with imines bearing different substituents on both the N- and C-sides of the imines. The second family is based on halogenated pyridinium salts which proved active with almost all considered imines. (Figure presented.).
- Weiss, Robin,Golisano, Tamara,Pale, Patrick,Mamane, Victor
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supporting information
p. 4779 - 4788
(2021/09/06)
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- Direct electrochemical reductive amination between aldehydes and amines with a H/D-donor solvent
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A novel electrochemical synthesis protocol has been achieved for reductive amination between aldehydes and amines in undivided cells at room temperature. Under metal-free and external-reductant-free electrolysis conditions, various important secondary amine products are obtained in moderate-to-high yields. Deuterium-labeling experiments have demonstrated that low-toxicity DMSO acts both as a solvent and a H-donor in the reaction. On this basis, various deuterium-labeled products with good-to-excellent D-incorporation have been synthesized by using DMSO-d6 as a solvent. Furthermore, a molecule with GR-antagonistic activity has been synthesized through further sulfonylation.
- Chen, Lu,Hong, Huanliang,Hu, Jinhui,Huang, Yubing,Li, Yibiao,Liang, Gen,Pu, Suyun,Zhu, Zhongzhi,Zou, Zirong
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supporting information
p. 5832 - 5837
(2020/11/03)
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- A Highly Selective Manganese-Catalyzed Synthesis of Imines under Phosphine-Free Conditions
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An efficient and highly selective phosphine-free NN-manganese(I) complex catalyst system was developed for the acceptorless dehydrogenative coupling of alcohols with amines to form imines. The coupling reactions underwent at 3 mol % catalyst loading, and a large range of alcohols and amines with diverse functional groups was applied, including challenging diol and diamine. The target imine products were obtained in good to excellent yields. The present work provides an alternative method to construct highly active nonprecious metal complex catalysts based on phosphine-free ligands.
- Chai, Huining,Yu, Kun,Liu, Bo,Tan, Weiqiang,Zhang, Guangyao
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p. 217 - 226
(2020/01/31)
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- Photoredox-Catalyzed Four-Component Reaction for the Synthesis of Complex Secondary Amines
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The one-pot sulfonylation/aminoalkylation of styrene derivatives furnishing substituted ?3-sulfonylamines was accomplished through a photoredox-catalyzed four-component reaction. Besides one molecule of water and the sodium counterion of the sulfinate, all atoms of the starting materials are transferred to the final product, rendering this process highly atom-efficient. The operationally simple protocol allows for the simultaneous formation of three new single bonds (C-S, C-N, and C-C) and therefore grants rapid access to structurally diverse products.
- Kammer, Lisa Marie,Krumb, Matthias,Spitzbarth, Benjamin,Lipp, Benjamin,Kühlborn, Jonas,Busold, Jonas,Mulina, Olga M.,Terentev, Alexander O.,Opatz, Till
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supporting information
p. 3318 - 3322
(2020/03/24)
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- Synthesis and Reactivity of Fluorinated Triaryl Aluminum Complexes
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The addition of the Grignard 3,4,5-ArFMgBr to aluminum(III) chloride in ether generates the novel triarylalane Al(3,4,5-ArF)3·OEt2. Attempts to synthesize this alane via transmetalation from the parent borane with trimethylaluminum gave a dimeric structure with bridging methyl groups, a product of partial transmetalation. On the other hand, the novel alane Al(2,3,4-ArF)3 was synthesized from the parent borane and trimethylaluminum. Interestingly, the solid-state structure of Al(2,3,4-ArF)3 shows an extended chain structure resulting from neighboring Al···F contacts. Al(3,4,5-ArF)3·OEt2 was then found to be an effective catalyst for the hydroboration of carbonyls, imines, and alkynes with pinacolborane.
- Ould, Darren M. C.,Carden, Jamie L.,Page, Rowan,Melen, Rebecca L.
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supporting information
p. 14891 - 14898
(2020/10/02)
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- Synthesis and molecular docking studies of imines as α-glucosidase and α-amylase inhibitors
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Imine functionality is found in many compounds with important biological activity. Thus, the development of novel synthetic approaches for imines is important. In this work, it is propose an easy, eco-friendly and straightforward synthesis pathway of aryl imines under microwave irradiation catalyzed by Alumina-sulfuric acid. In addition, the in vitro enzymatic inhibition, antioxidant activity and molecular docking studies were performed. The aryl imines were isolated with yields in the range of 37–94%. All aryl imines synthesized were evaluated for in vitro inhibitory potential against α-glucosidase and α-amylase enzymes and the results exhibited that the most of the compounds displayed inhibitory activity against both enzymes. The (E)-1-(4-nitrophenyl)-N-(pyridin-2-yl)methanimine (3d) was 1.15-fold more active than acarbose against α-amylase whilst the (E)-1-phenyl-N-(pyridin-2-yl)methanimine (3c) displayed similar activity that acarbose against α-glucosidase. The molecular docking studies in α-glucosidase and α-amylase reveal that aryl imines mainly establish an H-bond with the R2-subtituent and hydrophobic interactions with the R1-subtituent. The docking analysis reveals these synthetic aryl imines 3d-i interact in same active site than acarbose drug in both enzymes.
- Aispuro-Pérez, Analy,Bastidas, Pedro,Calderón-Zamora, Loranda,García-Páez, Fernando,López-ávalos, Juan,Monta?o, Sarita,Montes-Avila, Julio,Ochoa-Terán, Adrián,Osuna-Martínez, Ulises,Picos-Corrales, Lorenzo A.,Sarmiento-Sánchez, Juan I.
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- (S)-4-(4-aminobenzyl)-2-oxazolidinone based 2-azetidinones for antimicrobial application and luminescent sensing of divalent metal cations
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The impact of linezolid as an antibiotic against gram-positive bacteria has inspired synthetic chemists to use oxazolidinones as substrate molecule in the synthesis of newer scaffolds with important pharmacological implication. The oxazolidin-2-ones are key intermediates in the synthesis of many interesting biologically active compounds. Design and synthesis of a new series of (S)-4-(4-aminobenzyl)-2-oxazolidinone based multifunctional azetidinones were accomplished. Synthesis of the scaffolds was performed through a multi-step reaction process involving protection of amine functional group, conversion of protected (S)-4-(4-aminobenzyl)-2-oxazolidinone to its acetic acid derivative and then to acid chloride, and finally coupled with different substituted aromatic imines under mild reaction conditions in presence of an appropriate base. Structural characterization was carried out using conventional spectroscopic techniques. The compounds were screened for their antimicrobial activity against gram-positive and gram-negative bacteria and were found to possess better and promising antimicrobial property than some of the reported antimicrobial drugs like disulfonamide and tetracycline. Additionally, the scaffolds also exhibit prominent sensing property for divalent metal cations like Cu2+, Zn2+, and Ni2+, through fluorescence quenching effect.
- Baruah, Shyamal,Aier, Merangmenla,Puzari, Amrit
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p. 2498 - 2511
(2020/03/31)
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- Anil Synthesis in the Design of Push?Pull Systems. Synthesis of 2- and 4-(4-Styrylphenyl)-substituted Diphenylpyrimidines
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Abstract: The potential of anil synthesis for the preparation of 2,4,6-triaryl-substituted pyrimidines with an extended chain of delocalized π-bonds was studied. The reaction of (E)-3-phenyl-1-(p-tolyl)prop-2-en-1-one or chalcone with benzamidine, 4-methylbenzamidine, or 4-isobutoxybenzamidine hydrochlorides in ethanol in the presence of KOH gave 2,4-diphenyl-6-(p-tolyl)pyrimidine, 4,6-diphenyl-2-(p-tolyl)pyrimidine, and 2-(4-isobutoxyphenyl)-4-phenyl-6-(p-tolyl)pyrimidine. The synthesized pyrimidines were reacted with (E)-N-(phenyl- or 2-chlorophenyl)-1-arylmethanimines in DMF in the presence of a KOH/LiH mixture to obtain (E)-4,6-diphenyl-2-(4-styrylphenyl)pyrimidines and (E)-2,6-diphenyl-4-(4-styrylphenyl)pyrimidines were obtained.
- Danagulyan, G. G.,Gukasyan, G. T.,Harutyunyan, A. A.,Panosyan, H. A.,Safaryan, M. S.
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p. 269 - 275
(2020/04/21)
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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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- A niobium-catalyzed coupling reaction of α-keto acids with: Ortho -phenylenediamines: Synthesis of 3-arylquinoxalin-2(1 H)-ones
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A general methodology to access valuable 3-arylquinoxalin-2(1H)-ones was developed, by the reaction of α-keto acids with ortho-phenylenediamines in the presence of ammonium niobium oxalate (ANO) as a catalyst. The reactions were conducted in only 10 min under ultrasonic irradiation as an alternative energy source, affording water as the only co-product. A total of twenty-three different 3-arylquinoxalin-2(1H)-ones were selectively obtained in good to excellent yields by this atom-efficient protocol. Additionally, 1H-15N HMBC experiments were used to reveal the regioisomerism of the obtained products.
- Ebersol, Camila,Rocha, Nicole,Penteado, Filipe,Silva, Márcio S.,Hartwig, Daniela,Lenard?o, Eder J.,Jacob, Raquel G.
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supporting information
p. 6154 - 6160
(2019/11/20)
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- Micropores Induced Stereoselective Synthesis of E-imines: Synergistic Effect between Cerium Species and Micropores in CeAlPO-5 Molecular Sieves
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Metal-doped zeolitic microporous materials are often viewed as something extremely negative as catalysis for the reactions involving aromatic molecules because of severe diffusion limitation. For these reasons, many chemists aim to development of the large microporous or hierarchical micro-mesoporous zeolites as supports that allow for the access of the “bulky” reactants. But the “small” micropore with respect to an aromatic molecules-involving reaction is not always a negative point. Here we employed a hierarchical micro-mesoporous CeAlPO-5 molecular sieve (HP-CeAlPO-5) as the catalyst that can catalyze stereoselective synthesis of E-imines through the reaction of alcohols with amines. Control reactions, DFT calculations and GC-MS analyses demonstrated that the feature of the uniform “small” micropore in the HP-CeAlPO-5 catalyst play a key role in the stereoselective synthesis of E-imines. In addition, the reaction tolerates a broad range of alcohols and amines, and can be performed with as little as 0.89 mole percent catalyst in more than 90.6 percent yield and about 99.7 : 0.3 stereoselective ratio. This zeolitic catalyst provides a conceptually new and practical protocol to stereoselective synthesis of E-imine compounds.
- Jin, Yangxin,Cao, Yali,Fang, Guoyong,Ruan, Fei,Ke, Qingping
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p. 3178 - 3181
(2019/07/04)
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- Phosphine-Free Well-Defined Mn(I) Complex-Catalyzed Synthesis of Amine, Imine, and 2,3-Dihydro-1 H-perimidine via Hydrogen Autotransfer or Acceptorless Dehydrogenative Coupling of Amine and Alcohol
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The application of nontoxic, earth-abundant transition metals in place of costly noble metals is a paramount goal in catalysis and is especially interesting if the air- and moisture-stable ligand scaffold is used. Herein, we report the synthesis of amines/imines directly from alcohol and amines via hydrogen autotransfer or acceptorless dehydrogenation catalyzed by well-defined phosphine-free Mn complexes. Both imines and amines can be obtained from the same set of alcohols and amines using the same catalyst, only by tuning the reaction conditions. The amount and nature of the base are found to be a highly important aspect for the observed selectivity. Both the primary and secondary amines have been employed as substrates for the N-alkylation reaction. As a highlight, we showed the chemoselective synthesis of resveratrol derivatives. Furthermore, the Mn-catalyzed dehydrogenative synthesis of structurally important 2,3-dihydro-1H-perimidines has also been demonstrated. Density functional theory calculations were also carried out to model the reaction path and to calculate the reaction profile.
- Das, Kalicharan,Mondal, Avijit,Pal, Debjyoti,Srivastava, Hemant Kumar,Srimani, Dipankar
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supporting information
p. 1815 - 1825
(2019/04/30)
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- Amide bond synthesis via silver(I) N-heterocyclic carbene-catalyzed and tert-butyl hydroperoxide-mediated oxidative coupling of alcohols with amines under base free conditions
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We present a base free method for amide bond construction via oxidative coupling of alcohols with amines catalyzed by Silver(I) N-heterocyclic carbenes (Ag(I)-NHCs) and mediated by tert-butyl hydroperoxide (TBHP) in ethanol. The results of controlled experiments suggest that the oxidative coupling proceeds through the formation of aldehyde, then subsequent attack by amine to give hemiaminal, which can then be oxidized to amide.
- Balaboina, Ramesh,Thirukovela, Narasimha Swamy,Vadde, Ravinder,Vasam, Chandra Sekhar
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supporting information
p. 847 - 851
(2019/02/20)
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- Electrophilic [N—F]+ catalysed asymmetric allylation of (E)-N,1-diphenylmethanimine
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New efficient catalysts based on electrophilic N-fluoro quaternary ammonium salts are reported for catalytic allylation of (E)-N,1-diphenylmethanimine. The chiral version of the catalyst based on cinchonidine (F-CD-BF4) shows high catalytic activity with approximately 94% ee and TOF (>800?h?1). The F-CD-BF4 is prepared from cinchonidine and Selectfluor by one-step transfer fluorination.
- Sharma, Poonam,Sharma, Rakesh K.
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supporting information
p. 91 - 96
(2019/01/04)
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- Nucleophilic Imines and Electrophilic o-Quinone Methides, a Three-Component Assembly of Assorted 3,4-Dihydro-2 H-1,3-benzoxazines
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A one-pot method for joining three separate components leading to an assortment of N-substituted 3,4-dihydro-2H-1,3-benzoxazines is described. The method involves the addition of a Grignard reagent to an o-OBoc salicylaldehyde in the presence of an imine. With a variety of components, 15 examples are presented, including the diastereoselective incorporation of chiral imines.
- Chen, Peishan Kc,Wong, Yuk Fai,Yang, Derek,Pettus, Thomas R. R.
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supporting information
p. 7746 - 7749
(2019/10/11)
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- Acceptorless dehydrogenative construction of CN and CC bonds through catalytic aza-Wittig and Wittig reactions in the presence of an air-stable ruthenium pincer complex
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The construction of CN bonds was achieved by the dehydrogenative coupling of alcohol and azide via aza-Wittig type reaction. The reaction is catalyzed by an acridine-derived ruthenium pincer complex and does not use any oxidant. The present protocol offers a wide substrate scope, including aliphatic, aryl or heteroaryl alcohol/azides. This expeditious protocol was successfully applied to construct a CC bond directly from alcohol via dehydrogenative Wittig reaction. Furthermore, the synthesis of structurally important pyrrolo[1,4]benzodiazepine derivatives was also achieved by this methodology.
- Biswas, Nandita,Das, Kalicharan,Sardar, Bitan,Srimani, DIpankar
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p. 6501 - 6512
(2019/05/24)
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- Alcohol Amination Catalyzed by Copper Powder as a Self-Supported Catalyst
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Catalytic alcohol amination is a sustainable reaction for N-alkyl amine synthesis. Homogeneous and supported copper catalysts have long been studied for this reaction and have given some impressive results. In this study, copper powder is found to behave as an active catalyst for alcohol amination, giving better catalytic performance than metal-oxide-supported nanocopper catalysts. Catalyst characterization suggests that the copper powder can be considered as a self-supported nanocopper catalyst (i.e., nanocopper supported on copper particles). These results might promote the study of unsupported transition metal powders in sustainable catalytic reactions.
- Wu, Yajuan,Huang, Yongji,Dai, Xingchao,Shi, Feng
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p. 3185 - 3191
(2018/11/30)
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- Rhodium-catalyzed synthesis of imines and esters from benzyl alcohols and nitroarenes: Change in catalyst reactivity depending on the presence or absence of the phosphine ligand
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The [Rh(COD)Cl]2/xantphos/Cs2CO3 system efficiently catalyzes the reductive N-alkylation of aryl nitro compounds with alcohols by a borrowing-hydrogen strategy to afford the corresponding imine products in good to excellent yields. In the absence of xantphos, the [Rh(COD)Cl]2/Cs2CO3 catalytic system behaves as an effective catalyst for the dehydrogenative coupling of alcohols to esters, with nitrobenzene as a hydrogen acceptor. The reactivity of the rhodium catalytic system can be easily manipulated to selectively afford the imine or ester.
- Song, Taemoon,Park, Ji Eun,Chung, Young Keun
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p. 4197 - 4203
(2018/04/14)
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- A Revised Mechanism for the Kinugasa Reaction
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Detailed kinetic analysis for the Cu(I)-catalyzed Kinugasa reaction forming β-lactams has revealed an anomalous overall zero-order reaction profile, due to opposing positive and negative orders in nitrone and alkyne, respectively. Furthermore, the reaction displays a second-order dependence on the catalyst, confirming the critical involvement of a postulated bis-Cu complex. Finally, reaction progress analysis of multiple byproducts has allowed a new mechanism, involving a common ketene intermediate to be delineated. Our results demonstrate that β-lactam synthesis through the Kinugasa reaction proceeds via a cascade involving (3 + 2) cycloaddition, (3 + 2) cycloreversion, and finally (2 + 2) cycloaddition. Our new mechanistic understanding has resulted in optimized reaction conditions to dramatically improve the yield of the target β-lactams and provides the first consistent mechanistic model to account for the formation of all common byproducts of the Kinugasa reaction.
- Malig, Thomas C.,Yu, Diana,Hein, Jason E.
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supporting information
p. 9167 - 9173
(2018/07/15)
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- Resolving a Reactive Organometallic Intermediate from Dynamic Directing Group Systems by Selective C?H Activation
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Catalyst discovery from systems of potential precursors is a challenging endeavor. Herein, a new strategy applying dynamic chemistry to the identification of catalyst precursors from C?H activation of imines is proposed and evaluated. Using hydroacylation of imines as a model reaction, the selection of an organometallic reactive intermediate from a dynamic imine system, involving many potential directing group/metal entities, is demonstrated. The identity of the amplified reaction intermediate with the best directing group could be resolved in situ by ESI-MS, and coupling of the procedure to an iterative deconvolution protocol generated a system with high screening efficiency.
- Schaufelberger, Fredrik,Timmer, Brian J. J.,Ramstr?m, Olof
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supporting information
p. 101 - 104
(2018/01/08)
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- Synergistic Photoredox Catalysis and Organocatalysis for Inverse Hydroboration of Imines
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The first catalytic inverse hydroboration of imines with N-heterocyclic carbene (NHC) boranes has been realized by means of cooperative organocatalysis and photocatalysis. This catalytic combination provides a promising platform for promoting NHC-boryl radical chemistry under sustainable and radical-initiator-free conditions. The highly important functional-group compatibility and possible application in late-stage hydroborations represent an important step forward to an enhanced α-amino organoboron library.
- Zhou, Nengneng,Yuan, Xiang-Ai,Zhao, Yue,Xie, Jin,Zhu, Chengjian
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supporting information
p. 3990 - 3994
(2018/03/21)
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- Efficient Synthesis of Amines by Iron-Catalyzed C=N Transfer Hydrogenation and C=O Reductive Amination
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Here we report the catalytic transfer hydrogenation (CTH) of non-activated imines promoted by a Fe-catalyst in the absence of Lewis acid co-catalysts. Use of the (cyclopentadienone)iron complex 1, which is much more active than the classical ‘Kn?lker complex’ 2, allowed to reduce a number of N-aryl and N-alkyl imines in very good yields using iPrOH as hydrogen source. The reaction proceeds with relatively low catalyst loading (0.5–2 mol%) and, remarkably, its scope includes also ketimines, whose reduction with a Fe-complex as the only catalyst has little precedents. Based on this methodology, we developed a one-pot CTH protocol for the reductive amination of aldehydes/ketones, which provides access to secondary amines in high yield without the need to isolate imine intermediates. (Figure presented.).
- Facchini, Sofia Vailati,Cettolin, Mattia,Bai, Xishan,Casamassima, Giuseppe,Pignataro, Luca,Gennari, Cesare,Piarulli, Umberto
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supporting information
p. 1054 - 1059
(2018/01/27)
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- Photo-induced reductive cross-coupling of aldehydes, ketones and imines with electron-deficient arenes to construct aryl substituted alcohols and amines
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Umpolung reactions of C=X bonds (X = O, N) are valuable ways of constructing new C–C bonds, which are sometimes difficult to be constructed using traditional synthetic pathways. Classical polarity inversion of C=X bonds (X = O, N) usually requires air or moisture-sensitive and strong reducing agents, which limit the feasibility of substrate scope. Herein we describe a photo-induced reductive cross-coupling reaction of aldehydes, ketones and imines with electron-deficient arenes (aromatic nitriles) using fac-Ir(ppy)3 as a photocatalyst and diisopropylethylamine (DIPEA) as a terminal reductant under visible light irradiation. Mild conditions and high yields mean that this new polarity inversion strategy can be used with aryl-substituted alcohols and amines. Spectroscopic studies and control experiments have demonstrated the oxidative quenching of Ir(ppy)3* by electron-deficient arenes involved in the key step for the C–C bond formation.
- Liu, Zan,Nan, Xiaolei,Lei, Tao,Zhou, Chao,Wang, Yang,Liu, Wenqiang,Chen, Bin,Tung, Chenho,Wu, Lizhu
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p. 487 - 494
(2018/03/22)
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- Aerobic Oxidative Homo- and Cross-Coupling of Amines Catalyzed by Phenazine Radical Cations
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Phenazine radical cations (PhRCs) were used for the first time as efficient metal-free catalysts for the oxidative homo- and cross-coupling of a variety of different amines. A series of functional PhRCs were prepared, characterized with X-ray diffraction, and their radical character was investigated with DFT calculations. They were tested as catalysts under neat conditions with low oxygen pressure to prepare homo- and cross-coupled aliphatic and aromatic imines in high yields. Although all synthesized phenazines were catalytically active, the highest reaction rates and the best selectivity were achieved using the 5,10-dihydro-5,10-dimethylphenazine radical cation. By means of fluorescence, UV-vis and EPR spectroscopy, a mechanism of the oxidative amine coupling, catalyzed by PhRCs, is proposed.
- Bri?ar, Rok,Unglaube, Felix,Hollmann, Dirk,Jiao, Haijun,Mejía, Esteban
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p. 13481 - 13490
(2018/11/02)
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- Higher Order Constitutional Dynamic Networks: [2×3] and [3×3] Networks Displaying Multiple, Synergistic and Competitive Hierarchical Adaptation
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The present study investigates the constitutional dynamic networks (CDNs) underlying dynamic covalent libraries (DCLs) that extend beyond the [2×2] case toward higher orders, namely [2×3] and [3×3] CDNs involving respectively six and nine constituents generated from the recombination of five and six components linked through reversible chemical reactions. It explores the behavior of such systems under the action of one or two effectors. More specifically and for the sake of proof of principle, it makes use of DCLs involving dynamic organic ligands and analyzes their single and double adaptive response under the action of one and two metal cation effectors. Thus, interconversions within [2×3] DCLs of six constituents (hydrazone, acylhydrazone, and imine ligands) give access to the generation of [2×3] CDNs of 3D trigonal prismatic type consisting of three [2×2] sub-networks and presenting specific responses to the application of Cu+ and Zn2+ metal cation effectors, in particular double agonistic amplification. More complex [3×3] CDNs based on nine ligand constituents of imine, hydrazone, and acylhydrazone types were also designed and subjected to the application of one or two effectors, e.g., Cu+ and Fe2+ metal cations, revealing novel types of adaptive behavior: (i) agonistic amplification between a single constituent and a full [2×2] sub-network, and (ii) agonistic amplification along a single diagonal connecting three constituents. Of special interest is also the dependence of the response of the system to hierarchical sequence of effector application, whereby initial interaction with Cu+ ions results in the destruction of the network, whereas the sequence Fe2+ followed by Cu+ yields a clean three-constituent DCL. Finally and strikingly, the present results also demonstrate that the increase in complexity of the system by introduction of an additional entity leads to a simpler output through dynamic competition between components.
- Men, Guangwen,Lehn, Jean-Marie
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supporting information
p. 2474 - 2483
(2017/02/23)
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- C–H Bond Functionalization of 1,4-Benzoquinone by Silver-Mediated Regioselective Phosphination and Amination Reactions
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The one-pot synthesis of 2,5-bis(diarylphosphoryl)-3,6-bis(arylamino)cyclohexa-2,5-diene-1,4-diones has been achieved by AgI-mediated full C–H functionalization of 1,4-benzoquinone (BQ) through regioselective dual phosphination and amination reactions. BQ, diarylphosphine oxides [SPOs, Ar2PH(=O)], and imines reacted to give the products under mild conditions. 1,4-Naphthoquinone (NQ) could also be used instead of BQ. When aniline was used instead of the corresponding imine, a lower yield of the desired product was obtained. In the absence of Ag2CO3, hydrophosphinylation of the imine by the SPO occurred as a competitive side-reaction. AgI plays versatile roles in this reaction, as a mediator for facilitating the consecutive additions of Ar2P(=O)– and aniline to the related β-carbon atoms of BQ, as an oxidant of hydroquinone (HQ) intermediates to form the substituted BQ counterpart, and as an inhibitor of the hydrophosphinylation side-reaction of the imine by the SPO. The X-ray crystal structures of several new products have been determined. A reaction mechanism is also proposed based on the experimental results.
- Chang, Yu-Chang,Yuan, Pin-Ting,Hong, Fung-E
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p. 2441 - 2450
(2017/05/12)
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- β-Selective Reductive Coupling of Alkenylpyridines with Aldehydes and Imines via Synergistic Lewis Acid/Photoredox Catalysis
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Umpolung (polarity reversal) strategies of aldehydes and imines have dramatically expanded the scope of carbonyl and iminyl chemistry by facilitating reactions with non-nucleophilic reagents. Herein, we report the first visible light photoredox-catalyzed β-selective reductive coupling of alkenylpyridines with carbonyl or iminyl derivatives with the aid of a Lewis acid co-catalyst. Our process tolerates complex molecular scaffolds (e.g., sugar, natural product, and peptide derivatives) and is applicable to the preparation of compounds containing a broad range of heterocyclic moieties. Mechanistic investigations indicate that the key step involves single-electron-transfer reduction of aldehydes or imines followed by the addition of resulting ketyl or α-aminoalkyl radicals to Lewis acid-activated alkenylpyridines.
- Lee, Katarzyna N.,Lei, Zhen,Ngai, Ming-Yu
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supporting information
p. 5003 - 5006
(2017/05/04)
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- Quinone-catalyzed oxidative deformylation: Synthesis of imines from amino alcohols
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A new method for imine synthesis by way of quinone-catalyzed oxidative deformylation of 1, 2-amino alcohols is reported. A wide range of readily accessible amino alcohols and primary amines can be reacted to provide N-protected imine products. The methodology presented provides a novel organocatalytic approach for imine synthesis and demonstrates the synthetic versatility of quinone-catalyzed oxidative C-C bond cleavage.
- Liu, Xinyun,Phan, Johnny H.,Haugeberg, Benjamin J.,Londhe, Shrikant S.,Clift, Michael D.
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supporting information
p. 2895 - 2901
(2018/01/17)
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- Combination of Enabling Technologies to Improve and Describe the Stereoselectivity of Wolff-Staudinger Cascade Reaction
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A new, single-mode bench-top resonator was evaluated for the microwave-assisted flow generation of primary ketenes by thermal decomposition of α-diazoketones at high temperature. A number of amides and β-lactams were obtained by ketene generation in situ and reaction with amines and imines, respectively, in good to excellent yields. The preferential formation of trans-configured β-lactams was observed during the [2+2] Staudinger cycloaddition of a range of ketenes with different imines under controlled reaction conditions. Some insights into the mechanism of this reaction at high temperature are reported, and a new web-based molecular viewer, which takes advantage from Augmented Reality (AR) technology, is also described for a faster interpretation of computed data.
- Musio,Mariani,?liwiński,Kabeshov,Odajima,Ley
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supporting information
p. 3515 - 3526
(2016/10/18)
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- Enantioselective and Regiodivergent Functionalization of N-Allylcarbamates by Mechanistically Divergent Multicatalysis
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A pair of mechanistically divergent multicatalytic reaction sequences has been developed consisting of nickel-catalyzed isomerization of N-allylcarbamates and subsequent phosphoric-acid-catalyzed enantioselective functionalization of the resulting intermediates. By appropriate selection of reaction partners, in situ generated imines and ene-carbamates are mechanistically partitioned to yield opposing functionalized products. Formal α-functionalization to give protected α-arylamines is achieved upon enantioselective Friedel–Crafts reaction with arene nucleophiles, whereas formal β-functionalization is achieved upon reaction with diarylimine electrophiles in an enantioselective Povarov-[4+2] cycloaddition.
- Richmond, Edward,Khan, Ismat Ullah,Moran, Joseph
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supporting information
p. 12274 - 12277
(2016/08/24)
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- Pd(II)/Ag(I)-Promoted One-Pot Synthesis of Cyclic Ureas from (Hetero)Aromatic Amines and Isocyanates
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A simple and facile one-pot reaction has been developed to afford a diverse range of N,N′-disubstituted benzimidazolones and imidazopyridinones containing two differently substituted N atoms. A cooperative Pd(II)/Ag(I) system promotes the sequential addition/intramolecular C-H amidation reaction of (hetero)aromatic amines and isocyanates, leading to the formation of two C-N bonds. A mechanism involving radical intermediates generated by single-electron transfer (SET) in the presence of a Ag2CO3 oxidant and Pd(OAc)2 Lewis acid is proposed. This protocol offers an operationally easy, simple, and robust approach with the use of readily available starting materials, good functional group tolerance, and high efficiency.
- Youn, So Won,Kim, Yi Hyun
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supporting information
p. 6140 - 6143
(2016/12/09)
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- Scalable synthesis of secondary and tertiary amines by heterogeneous Pt-Sn/γ-Al2O3catalyzed N-alkylation of amines with alcohols
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Synthesis of secondary and tertiary amines has been efficiently realized from the N-alkylation of amines with alcohols by means of heterogeneous bimetallic Pt-Sn/γ-Al2O3catalyst (0.5?wt % Pt, molar ratio Pt:Sn?=?1:3) through a borrowing hydrogen strategy. The Pt-Sn/γ-Al2O3catalyst has exhibited very high catalytic activity towards a wide range of amines and alcohols, and can be conveniently recycled without Pt metal leaching. The present protocol was applied for the synthesis of N-phenylbenzylamine in 96% isolated yield from aniline and benzyl alcohol on a 2.1?kg scale of the substrates, demonstrating its potential applicability for higher-order amine synthesis.
- Wu, Kaikai,He, Wei,Sun, Chenglin,Yu, Zhengkun
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supporting information
p. 8516 - 8521
(2016/11/28)
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- Isomerization method for bis(amino-methyl)cyclohexane
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An isomerization method for bis(amino-methyl)cyclohexane has an isomerization step for isomerizing bis(amino-methyl)cyclohexane in the presence of an imine compound represented by general formula (1) and one or more type of compound selected from the group comprising an alkali metal, an alkali-metal-containing compound, an alkali earth metal, and an alkali-earth-metal-containing compound. (In general formula (1), R1 and R2 each independently indicates a monovalent group selected from the group comprising a hydrogen atom, a substituted or un-substituted hydrocarbon group, a substituted or un-substituted alkoxy group, and an acyl group. (R1 and R2 may be bonded to each other and form a ring.) R3 indicates an n-valent group selected from the group comprising a hydrogen atom and a substituted or un-substituted hydrocarbon group, n being an integer from 1 to 10.).
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Paragraph 0250; 0251; 0252
(2016/10/10)
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- Iron-Carbonyl-Catalyzed Redox-Neutral [4+2] Annulation of N-H Imines and Internal Alkynes by C-H Bond Activation
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Stoichiometric C-H bond activation of arenes mediated by iron carbonyls was reported by Pauson as early as in 1965, yet the catalytic C-H transformations have not been developed. Herein, an iron-catalyzed annulation of N-H imines and internal alkynes to furnish cis-3,4-dihydroisoquinolines is described, and represents the first iron-carbonyl-catalyzed C-H activation reaction of arenes. Remarkablely, this is also the first redox-neutral [4+2] annulation of imines and alkynes proceeding by C-H activation. The reaction also features only cis stereoselectivity and excellent atom economy as neither base, nor external ligand, nor additive is required. Experimental and theoretical studies reveal an oxidative addition mechanism for C-H bond activation to afford a dinuclear ferracycle and a synergetic diiron-promoted H-transfer to the alkyne as the turnover-determining step. Double dose of iron: The titled redox-neutral [4+2] annulations to furnish cis-3,4-dihydroisoquinolines were achieved by using iron catalysis. Mechanistic studies show the synergy of dinuclear iron in the C-H bond activation and turnover-limiting hydrogen-transfer steps. The reaction demonstrates excellent atom economy and exclusive cis stereoselectivity.
- Jia, Teng,Zhao, Chongyang,He, Ruoyu,Chen, Hui,Wang, Congyang
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supporting information
p. 5268 - 5271
(2016/04/26)
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- Solvent-free synthesis of azomethines, spectral correlations and antimicrobial activities of some E-benzylidene-4-chlorobenzenamines
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Some azomethines including substituted benzylidene-4-chlorobenzenamines (E-imines) have been synthesized by fly-ash: PTS catalyzed microwave assisted condensation of 4-chloroaniline and substituted benzaldehydes under solvent-free conditions. The yield of the imines has been found to be more than 85%. The purity of all imines has been checked using their physical constants and UV, IR and NMR spectral data. These spectral data have been correlated with Hammett substituent constants and F and R parameters using single and multi-linear regression analysis. From the results of statistical analysis, the effect of substituents on the above spectral data has been studied. The antimicrobial activities of all imines have been studied using standard methods.
- Suresh,Sakthinathan,Kamalakkannan,Ranganathan,Sathiyamoorthi,Mala,Arulkumaran,Vijayakumar,Sundararajan,Vanangamudi,Subramanian,Thirunarayanan,Vanaja,Kanagambal
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p. 275 - 290
(2015/07/27)
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- Stereoselective peterson olefinations from bench-stable reagents and N-phenyl imines
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The synthesis of bench-stable α,α-bis(trimethylsilyl)toluenes and tris(trimethylsilyl)methane is described and their use in stereoselective Peterson olefinations has been achieved with a wide substrate scope. Product stereoselectivity was poor with carbonyl electrophiles (E/Z ~1:1 to 4:1) though this was significantly improved by employing the corresponding substituted N-benzylideneaniline (up to 99:1) as an alternative electrophile. The olefination byproduct was identified as N,N-bis(trimethylsilyl)aniline and could be easily separated from product by aqueous acid extraction. Evidence for an autocatalytic cycle has been obtained.
- Das, Manas,Manvar, Atul,Jacolot, Ma?wenn,Blangetti, Marco,Jones, Roderick C.,O'Shea, Donal F.
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supporting information
p. 8737 - 8740
(2015/06/08)
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- Development of Method for Amide Bond Formation via Metal-Free Aerobic Oxidative Amination of Aldehydes
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The present invention relates to a method for preparing an amide compound by using an aerobic oxidative amination reaction using an oxygen resource as an oxidizer in an organic solvent without metal by using a cyanide as a catalyst. An expensive metal catalyst is not needed to prepare the amide compound of the present invention. Therefore, the amide compound does not have a problem of toxicity caused by remaining metal and has excellent economic efficiency of atoms. Moreover, the amide compound can be used for industries in an easy manner because complicated processes such as a strong acid, low temperatures, and anhydrous conditions are not needed to prepare the amide compound.COPYRIGHT KIPO 2015
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Paragraph 0091
(2016/11/17)
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- Ruthenium-catalyzed double-fold C-H tertiary alkoxycarbonylation of arenes using di-tert-butyl dicarbonate
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An efficient ruthenium-catalyzed double-fold C-H alkoxycarbonylation of arenes was developed using di-tert-butyl dicarbonate as the tertiary esterification reagent, which leads to a direct route to valuable 2,6-dicarboxylated products. This journal is
- Hong, Xiaohu,Wang, Hao,Liu, Bingxin,Xu, Bin
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supporting information
p. 14129 - 14132
(2014/12/11)
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- Mn-catalyzed three-component reactions of imines/nitriles, grignard reagents, and tetrahydrofuran: An expedient access to 1,5-amino/keto alcohols
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An expedient Mn-catalyzed three-component synthesis of 1,5-amino/keto alcohols from Grignard reagents, imines/nitriles, and tetrahydrofuran (THF) is described, which deviates from the classic Grignard addition to imines/nitriles in THF solvent. THF is split and sewn in an unprecedented manner in the reaction, leading to the formation of two geminal C-C bonds via C-H and C-O cleavage. Mechanistic experiments and DFT calculations reveal radical and organo-Mn intermediates in the catalytic cycle and the α-arylative ring-opening of THF as the key reaction step.
- He, Ruoyu,Jin, Xiqing,Chen, Hui,Huang, Zhi-Tang,Zheng, Qi-Yu,Wang, Congyang
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supporting information
p. 6558 - 6561
(2014/05/20)
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- Stereoselective synthesis of α-alkylidene β-oxo amides by palladium-catalyzed carbonylation
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A direct method to obtain α-alkylidene β-oxo amides by the palladium-catalyzed carbonylation of α-chloro ketones in the presence of aromatic imines has been described. The methodology can be applied to a variety of C-aryl imines bearing N-aryl or N-alkyl substituents. The entire process is highly stereoselective and affords the α-alkylidene β-oxo amides only as (Z) isomers. A mechanistic hypothesis involving an acyl-β-lactam intermediate has also been proposed.
- Perrone, Serena,Salomone, Antonio,Caroli, Antonio,Falcicchio, Aurelia,Citti, Cinzia,Cannazza, Giuseppe,Troisi, Luigino
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p. 5932 - 5938
(2015/03/30)
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- Ionic-liquid-assisted metal-free oxidative coupling of amines to give imines
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An oxidative coupling of amines to give imines in ionic liquids (ILs) under metal-free aerobic conditions has been developed. The high efficiency achievable in ILs is mechanistically explained in terms of activation of the starting materials (benzylamine and molecular oxygen) by an initial electron transfer, promoted by the ionic nature of the solvent. Reactivity data of variously p-substituted benzylamines show a general deactivating effect, which would imply a change in the rate-determining step in the reaction mechanism.
- Monopoli, Antonio,Cotugno, Pietro,Iannone, Francesco,Ciminale, Francesco,Dell'Anna, Maria Michela,Mastrorilli, Piero,Nacci, Angelo
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supporting information
p. 5925 - 5931
(2015/03/30)
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- Aerobic oxidative coupling of alcohols and amines over Au-Pd/resin in water: Au/Pd molar ratios switch the reaction pathways to amides or imines
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A facile switch of the reaction pathways of aerobic oxidative coupling of alcohols and amines from amidation to imination was realized for the first time by tuning the Au/Pd ratios in ion-exchange resin supported Au-Pd alloy catalysts (Au-Pd/resin). Amides were obtained with high yields on Au6Pd/resin while imines were obtained over AuPd4/resin. Various alcohols and amines underwent oxidative coupling smoothly in water to afford the desired products with good to excellent yields. Further investigation on the reaction mechanism suggested the synergistic effect between Au and Pd determined the adsorption strength of the aldehyde intermediate, which in turn dictated the reaction pathways. That is, on Au-rich alloys (e.g., Au6Pd) absorbed aldehyde species was formed, followed by further oxidation to yield amides, while on Pd-rich alloys (e.g., AuPd4), free aldehyde was generated, which then underwent condensation with amines to produce imines. The discovery might provide avenues to develop new efficient catalysts for the green synthesis of special chemicals.
- Zhang, Leilei,Wang, Wentao,Wang, Aiqin,Cui, Yitao,Yang, Xiaofeng,Huang, Yanqiang,Liu, Xiaoyan,Liu, Wengang,Son, Jin-Young,Oji, Hiroshi,Zhang, Tao
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supporting information
p. 2680 - 2684
(2013/10/08)
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- Turning-on the quenched fluorescence of azomethines through structural modifications
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A series of fluorene azomethines were prepared to examine the effect of structural modification on the absolute fluorescence quantum yields (Φfl). The change in fluorescence occurring upon reversing the orientation of the azomethine bond, the number of fluorene units, and alkylation at the 9,9′-positions of fluorene was examined. It was found that Φfl could be tailored with these structural modifications with 0.05 ≤ Φfl ≤ 0.45. The highest Φfl was measured for the trimer derived from 2,7-diamino fluorene with each fluorene being alkylated at the 9,9′-positions. The fluorescence quantum yields did not increase at 77 K, implying the absence of fluorescence quenching modes involving internal conversion. Fluorescence enhancement was also not observed upon protonating the imine with trifluoroacetic acid. This confirms that Waldon inversion and isomerization are not fluorescence deactivation modes. Additionally, no photoisomerization was observed either at room temperature or at 77 K when the fluorene derivatives were irradiated at 354 nm. In contrast, the Z photoisomer of a N-benzylideneaniline analogue was spectroscopically detected both by absorbance and by 1H NMR spectroscopy. The absolute fluorescence quantum yield of conjugated azomethines was increased to 45 % by structural modifications and adjusting the orientation of the azomethines. Copyright
- Barik, Satyananda,Skene, William G.
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p. 2563 - 2572
(2013/06/04)
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