- Iridium(I)-Catalyzed Asymmetric Hydrogenation of Prochiral Imines; Protic Amines as Catalyst Improvers
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A catalytic system, Ir(I)-BINAP-protic amine, was found to be effective for asymmetric hydrogenation of imines and the highest enatioselectivity of 90percent ee has been attained for the hydrogenation of the cyclic imine, 2-phenyl-3,4,5,6-tetrahydropyridine.
- Tani, Kazuhide,Onouchi, Jun-ichiro,Yamagata, Tsuneaki,Kataoka, Yasutaka
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- Application of phosphine-oxazoline ligands in Ir-catalyzed asymmetric hydrogenation of acyclic aromatic N-arylimines
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(Chemical Equation Presented) A new class of chiral phosphine-oxazoline ligands have been developed. Chiral Ir complexes prepared from these ligands induced high enantioselectivities (66-90% ee) when applied to the asymmetric hydrogenation of acyclic aromatic N-arylimines.
- Triforiova, Anna,Diesen, Jarle S.,Chapman, Christopher J.,Andersson, Pher G.
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- A practical synthesis of enantiomerically pure N-benzyl-α-methyl benzylamine
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Optically pure (R)- and (S)N-benzyl-α-methyl benzylamine have been prepared on pilot plant scale from benzaldehyde and α-phenyl-ethylamine via palladium-catalyzed hydrogenation of the intermediate (R)-benzylidene-(1-phenylethyl)amine.
- Huckabee, Brian K.,Lin, Sechoing,Smith, Traci L.,Stuk, Timothy L.
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- Phosphines versus phosphinites as ligands in the rhodium catalyzed asymmetric hydrogenation of imines: A systematic study
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The asymmetric hydrogenation of N-(1-phenylethylidene)benzylamine with a range of rhodium(I)-diphosphine and diphosphinite catalysts is studied. The reaction is strongly sensitive to the size of the metal chelate. Complexes based on five- and six-membered chelates or electron-rich alkylphosphines gave poor or moderate conversions. The reactivity of diphosphine catalysts could be increased by the addition of p-toluenesulfonic acid. Unexpectedly, Rh-complexes based on chiral diphosphinites and a diphosphite also rapidly converted the substrate to the desired amine. Highest efficiency was observed with a rhodium(I) complex with (R,R)-1,2-cyclohexanol-bisdiphenylphosphinite [(R,R)-bdpch] as chiral ligand. Without any additive complete hydrogenation of the imine was achieved within 5 h. The product was produced in an enantioselectivity of 71%.
- Tararov, Vitali I.,Kadyrov, Renat,Riermeier, Thomas H.,Holz, Jens,Boerner, Armin
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- Iridium-Catalyzed Enantioselective Hydrogenation of Imines with Xylose Diphosphite and Diphosphinite Ligands
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Iridium complexes incorporating xylose diphosphinite 1 and diphosphite 2, 3 ligands as source of chirality are active catalysts for the hydrogenation of imines providing moderate ee. The enantioselectivity depends on the fine tuning of the structural parameters of the ligand and on the effect of additives.
- Guiu, Ester,Mu?oz, Bianca,Castillón, Sergio,Claver, Carmen
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- Asymmetric thermal transformation, a new way to enantiopure biphenyl- bridged titanocene and zirconocene complexes: Efficient catalysts for asymmetric imine hydrogenation
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Enantiopure biphenyl-bridged titanocene and zirconocene complexes were obtained, by an asymmetric thermal transformation of the binaphthol complexes formed from the metallocene racemates and subsequent transformation to the corresponding dichlorides, in practically quantitative yields. Increased rates of this transformation in the presence of O2 gas or TEMPO indicate a radical reaction mechanism. The biphenyl-bridged titanocene enantiomers give rise to an efficient asymmetric catalysis for the hydrogenation of cyclic and noncyclic imines.
- Ringwald, Markus,Stürmer, Rainer,Brintzinger, Hans H.
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- Efficient enantioselective hydrogenation of arylimines using aminophosphine-oxazoline iridium catalysts
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The preparation and characterization of cationic iridium complexes bearing chiral aminophosphine-oxazoline auxiliaries of general formula [Ir(COD)L*]X [X: PF6 and B(ArF)4] is reported. These complexes have been applied to the asymmetric hydrogenation of two imines: N-(phenylethylidene)aniline S1 and N-(phenylethylidene)benzylamine S2 providing the corresponding chiral amines in up to 90% and 82% ee, respectively.
- Blanc, Catherine,Agbossou-Niedercorn, Francine,Nowogrocki, Guy
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- Application of Transmetalation to the Synthesis of Planar Chiral and Chiral-at-Metal Iridacycles
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Diastereoselective lithiation of (S)-2-ferrocenyl-4-(1-methylethyl)oxazoline, followed by addition of HgCl2, resulted in the formation by transmetalation of an (S,Sp)-configured mercury substituted complex. Addition to this of [Cp?IrCl2]2 and tetrabutylammonium chloride resulted in a second transmetalation reaction and formation of an (S,Sp,RIr)-configured chloride-substituted half-sandwich iridacycle as exclusively a single diastereoisomer. By reversing the lithiation diastereoselectivity by use of a deuterium blocking group, an alternative (S,Rp,SIr)-configured iridacycle was synthesized similarly. Use of (R)-Ugi's amine as substrate in the lithiation/double transmetalation sequence gave an (R,Sp,SIr)-configured half-sandwich iridacycle, complexes of this type being previously unavailable by direct cycloiridation. Lithium to gold transmetalation was also demonstrated with the synthesis of an (S,Sp)-configured Au(I) ferrocenyloxazoline derivative. Use of the (S,Rp,SIr)-iridacycle as a catalyst for the formation of a chiral product by reductive amination with azeotropic HCO2H/NEt3 resulted in a racemate.
- Arthurs, Ross A.,Hughes, David L.,Horton, Peter N.,Coles, Simon J.,Richards, Christopher J.
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- A novel ruthenium-catalyzed amination of primary and secondary alcohols
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An improved method for the N-alkylation of primary amines with primary and secondary alcohols has been developed. Novel, effective catalyst systems, for example, Ru3(CO)12 combined with tri-o-tolylphosphine or n-butyl-di-1-adamantylphosphine, allow for aminations in a good yield under comparatively mild conditions.
- Tillack, Annegret,Hollmann, Dirk,Michalik, Dirk,Beller, Matthias
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- Mechanistic investigation on the hydrogenation of imines by [p-(Me 2CH)C6H4Me]RuH(NH2CHPhCHPhNSO 2C6H4-p-CH3). Experimental support for an ionic pathway
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The need for acidic activation in the stoichiometric hydrogenation of benzyl-[1-phenyl-ethylidene]-amine (6a) or [1-(4-methoxy-phenyl)-ethylidene]- methyl-amine (6b) by Noyori's catalyst [p-(Me2CH)C6H 4Me]RuH(NH2CHPhCHPhNSO2C6H 4-p-CH3) (2) is inconsistent with the proposed concerted mechanism and supports an ionic mechanism. The Royal Society of Chemistry 2006.
- Aberg, Jenny B.,Samec, Joseph S. M.,Baeckvall, Jan-E.
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- Identification of new catalysts for the asymmetric reduction of imines into chiral amines with polymethylhydrosiloxane using high-throughput screening
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The use of high-throughput techniques allowed the rapid identification of new catalysts for the enantioselective reduction of imines using polymethylhydrosiloxane (PMHS) as a reducing agent. By a simple modification of the chiral ligand structure that came out of the screening, the enantioselectivity of the reduction was increased from 40% ee to 60% ee.
- Ireland, Tania,Fontanet, Fran?ois,Tchao, Guen-Gnanh
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- Synthesis of polymer microspheres functionalized with chiral ligand by precipitation polymerization and their application to asymmetric transfer hydrogenation
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Monodisperse, crosslinked poly(divinylbenzene) and poly(methacrylic acid-co-ethylene glycol dimethacrylate) microspheres with (1R,2R)-N 1-toluenesulfonyl-1,2-diphenylethylene-1,2-diamine ((R,R)-TsDPEN) moiety were successfully prepared by precipitation polymerization. Introduction site of the (R,R)-TsDPEN moiety into the polymer microspheres could be controlled by changing the order of addition of the corresponding monomers. The functionalized polymer microspheres were applied to asymmetric transfer hydrogenation of ketone and imine. Polymer microsphere-supported chiral catalysts showed good reactivity and enantioselectivity in the catalytic asymmetrie transfer hydrogenations. Chiral secondary alcohol was quantitatively obtained with 94% ee in the asymmetric transfer hydrogenation of acetophenone in water. We also found that introduction site of the chiral catalyst and hydrophobiclty of the microspheres, as well as degree of the crosslinking, affected the yield and enantioselectivity of chiral product in this reaction.
- Haraguchi, Naoki,Nishiyama, Akihiro,Itsuno, Shinichi
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- Enantioselective Hydrogenation of Imines Using a Diverse Library of Ruthenium Dichloride(diphosphine)(diamine) Precatalysts
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A range of aromatic and cyclic imines were subjected to asymmetric hydrogenation with catalysts derived from complexes of the type RuCl 2(diphosphine)(diamine). Good to high enantioselectivities were observed. For each imine, a library of chiral complexes based on different diphosphine and diamine combinations was screened. A different combination of diphosphine and diamine was required each time to obtain the optimum enantioselectivity.
- Cobley, Christopher J.,Henschke, Julian P.
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- Switching Selectivity in Copper-Catalyzed Transfer Hydrogenation of Nitriles to Primary Amine-Boranes and Secondary Amines under Mild Conditions
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A simple and efficient copper-catalyzed selective transfer hydrogenation of nitriles to primary amine-boranes and secondary amines with an oxazaborolidine-BH3 complex is reported. The selectivity control was achieved under mild conditions by switching the solvent and the copper catalysts. More than 30 primary amine-boranes and 40 secondary amines were synthesized via this strategy in high selectivity and yields of up to 95%. The strategy was applied to the synthesis of 15N labeled in 89% yield.
- Song, Hao,Xiao, Yao,Zhang, Zhuohua,Xiong, Wanjin,Wang, Ren,Guo, Liangcheng,Zhou, Taigang
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p. 790 - 800
(2022/01/11)
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- Prolinol as a Chiral Auxiliary in Organophosphorus Chemistry
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Several strategies for the development of the synthesis of P-chiral organophosphorus compounds with (L)-prolinol as a source of chirality have been examined. A reaction of L-prolinol with a set of different alkyl/arylphosphonous acid diamides led in most of the cases to the quantitative formation of the appropriate bicyclic oxazaphospholidines with complete diastereo and enantioselectivity. The latter were reacted with BH3 complex and the formed borane analogues were submitted to structural modifications leading to tertiary phosphine-boranes. Additionally, the effectiveness of oxazaphospholidines as ligands in transition metal asymmetric catalysis has been tested in hydrogenation of dehydroaminoacid esters and imine.
- Kozio?, Anna E.,W?odarczyk, Adam
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p. 1931 - 1941
(2021/04/06)
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- Zirconium Catalyzed Hydroaminoalkylation for the Synthesis of α-Arylated Amines and N-Heterocycles
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The zirconium catalyzed hydroaminoalkylation of alkenes with N-aryl- and sterically demanding N-alkyl-α-arylated secondary amines by using commercially available Zr(NMe2)4 is reported. N-phenyl- and N-isopropylbenzylamine are used as amine substrates to establish the alkene substrate scope. Exclusively linear products are obtained in the presence of bulky vinylsilanes. Challenging α-heteroarylated amines and functionalized alkene substrates are compatible with this easy to use catalyst, affording a new disconnection strategy for the atom- and step-economic preparation of selectively substituted saturated α-arylated heterocycles.
- Koperniku, Ana,Schafer, Laurel L.
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supporting information
p. 6334 - 6339
(2021/03/08)
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- Hydrosilylation and Mukaiyama aldol-type reaction of quinolines and hydrosilylation of imines catalyzed by a mesoionic carbene-stabilized borenium ion
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Aldimines and ketimines containing electron-donating and electron-withdrawing groups can be hydrosilylated with borenium catalysts at as low as 1 mol% catalyst loading at room temperature, providing the corresponding secondary amines in excellent yields. Reactions with 2-phenylquinoline gave the 1,4-hydrosilylquinoline product selectively which can be further functionalized in a one-pot synthesis to give unique γ-amino alcohol derivatives. Control experiments suggest that the borenium ion catalyzes both the hydrosilylation and subsequent addition to the aldehyde.
- Bestvater, Brian P.,Clarke, Joshua J.,Crudden, Cathleen M.,DeJesus, Joseph F.,Devaraj, Karthik,Eisenberger, Patrick,Kojima, Ryoto
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supporting information
p. 6786 - 6791
(2021/08/20)
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- Cleavage∕cross-coupling strategy for converting β-O-4 linkage lignin model compounds into high valued benzyl amines via dual C–O bond cleavage
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Lignin is the most recalcitrant of the three components of lignocellulosic biomass. The strength and stability of the linkages have long been a great challenge for the degradation and valorization of lignin biomass to obtain bio-fuels and commercial chemicals. Up to now, the selective cleavage of C–O linkages of lignin to afford chemicals contains only C, H and O atoms. Our group has developed a cleavage/cross-coupling strategy for converting 4-O-5 linkage lignin model compounds into high value-added compounds. Herein, we present a palladium-catalyzed cleavage/cross-coupling of the β-O-4 lignin model compounds with amines via dual C–O bond cleavage for the preparation of benzyl amine compounds and phenols.
- Jia, Le,Li, Chao-Jun,Zeng, Huiying
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- Copper-catalyzed enantioselective carbonylation toward α-chiral secondary amides
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Secondary amides are omnipresent structural motifs in peptides, natural products, pharmaceuticals, and agrochemicals. The copper-catalyzed enantioselective hydroaminocarbonylation of alkenes described in this study provides a direct and practical approach for the construction of α-chiral secondary amides. An electrophilic amine transfer reagent possessing a 4-(dimethylamino)benzoate group was the key to the success. This method also features broad functional group tolerance and proceeds under very mild conditions, affording a set of α-chiral secondary amides in high yields (up to 96% yield) with unprecedented levels of enantioselectivity (up to >99% ee). α,β-Unsaturated secondary amides can also be produced though the method by using alkynes as the substrate.
- Wu, Xiao-Feng,Yuan, Yang,Zhao, Fengqian
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p. 12676 - 12681
(2021/10/19)
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- Highly economical and direct amination of sp3carbon using low-cost nickel pincer catalyst
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Developing more efficient routes to achieve C-N bond coupling is of great importance to industries ranging from products in pharmaceuticals and fertilizers to biomedical technologies and next-generation electroactive materials. Over the past decade, improvements in catalyst design have moved synthesis away from expensive metals to newer inexpensive C-N cross-coupling approaches via direct amine alkylation. For the first time, we report the use of an amide-based nickel pincer catalyst (1) for direct alkylation of amines via activation of sp3 C-H bonds. The reaction was accomplished using a 0.2 mol% catalyst and no additional activating agents other than the base. Upon optimization, it was determined that the ideal reaction conditions involved solvent dimethyl sulfoxide at 110 °C for 3 h. The catalyst demonstrated excellent reactivity in the formation of various imines, intramolecularly cyclized amines, and substituted amines with a turnover number (TON) as high as 183. Depending on the base used for the reaction and the starting amines, the catalyst demonstrated high selectivity towards the product formation. The exploration into the mechanism and kinetics of the reaction pathway suggested the C-H activation as the rate-limiting step, with the reaction second-order overall, holding first-order behavior towards the catalyst and toluene substrate.
- Brandt, Andrew,Rangumagar, Ambar B.,Szwedo, Peter,Wayland, Hunter A.,Parnell, Charlette M.,Munshi, Pradip,Ghosh, Anindya
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p. 1862 - 1874
(2021/01/20)
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- Chiral cyclometalated iridium complexes for asymmetric reduction reactions
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A series of chiral cyclometalated iridium complexes have been synthesised by cyclometalating chiral 2-aryl-oxazoline and imidazoline ligands with [Cp?IrCl2]2. These iridacycles were studied for asymmetric transfer hydrogenation reactions with formic acid as the hydrogen source and were found to display various activities and enantioselectivities, with the most effective ones affording up to 63% ee in the asymmetric reductive amination of ketones and 77% ee in the reduction of pyridinium ions. This journal is
- Smith, Jennifer,Kacmaz, Aysecik,Wang, Chao,Villa-Marcos, Barbara,Xiao, Jianliang
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supporting information
p. 279 - 284
(2021/01/18)
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- Cross-linked cyclodextrins bimetallic nanocatalysts: Applications in microwave-assisted reductive aminations
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The optimization of sustainable protocols for reductive amination has been a lingering challenge in green synthesis. In this context, a comparative study of different metal-loaded cross-linked cyclodextrins (CDs) were examined for the microwave (MW)-assisted reductive amination of aldehydes and ketones using either H2 or formic acid as a hydrogen source. The Pd/Cu heterogeneous nanocatalyst based on Pd (II) and Cu (I) salts embedded in a β-CD network was the most efficient in terms of yield and selectivity attained. In addition, the polymeric cross-linking avoided metal leaching, thus enhancing the process sustainability; good yields were realized using benzylamine under H2. These interesting findings were then applied to the MW-assisted one-pot synthesis of secondary amines via a tandem reductive amination of benzaldehyde with nitroaromatics under H2 pressure. The formation of a CuxPdy alloy under reaction conditions was discerned, and a synergic effect due to the cooperation between Cu and Pd has been hypothesized. During the reaction, the system worked as a bifunctional nanocatalyst wherein the Pd sites facilitate the reduction of nitro compounds, while the Cu species promote the subsequent imine hydrogenation affording structurally diverse secondary amines with high yields.
- Acciardo, Elisa,Cravotto, Giancarlo,Gaudino, Emanuela Calcio,Manzoli, Maela,Tabasso, Silvia,Varma, Rajender S.
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- Cine-Silylative Ring-Opening of α-Methyl Azacycles Enabled by the Silylium-Induced C-N Bond Cleavage
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Described herein is the development of a borane-catalyzed cine-silylative ring-opening of α-methyl azacycles. This transformation involves four-step cascade processes: (i) exo-dehydrogenation of alicyclic amine, (ii) hydrosilylation of the resultant enamine, (iii) silylium-induced cis-β-amino elimination to open the ring skeleton, and (iv) hydrosilylation of the terminal olefin. The present borane catalysis also works efficiently for the C-N bond cleavage of acyclic tertiary amines. On the basis of experimental and computational studies, the silicon atom was elucidated to play a pivotal role in the β-amino elimination step.
- Zhang, Jianbo,Chang, Sukbok
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p. 12585 - 12590
(2020/08/21)
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- Efficient One-Pot Reductive Aminations of Carbonyl Compounds with Aquivion-Fe as a Recyclable Catalyst and Sodium Borohydride
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A one-pot reductive amination of aldehydes and ketones with NaBH4 was developed with a view to providing efficient, economical and greener synthetic conditions. A recyclable iron-based Lewis catalyst, Aquivion-Fe, was used to promote imine formation in cyclopentyl methyl ether, followed by the addition of a small amount of methanol to the reaction mixture to enable C=N reduction by NaBH4. The protocol, applied to a wide number of amines and carbonyl compounds, resulted in ever complete conversion of these latter with excellent chemoselectivity towards the expected amination products in the most cases. Isolated yields, determined for a selection of the screened substrates, were found consistent with the previously obtained conversion and selectivity data. Cinacalcet, an important active pharmaceutical ingredient, was efficiently prepared by the title procedure.
- Airoldi, Veronica,Piccolo, Oreste,Roda, Gabriella,Appiani, Rebecca,Bavo, Francesco,Tassini, Riccardo,Paganelli, Stefano,Arnoldi, Sebastiano,Pallavicini, Marco,Bolchi, Cristiano
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supporting information
p. 162 - 168
(2019/12/11)
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- Iridium complexes with a new type of N^N′-donor anionic ligand catalyze the N-benzylation of amines via borrowing hydrogen
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The development of efficient and eco-friendly methods for the synthesis of elaborate amines is highly desired as they are valuable chemicals. The catalytic alkylation of amines using alcohols as alkylating agents, through the so-called borrowing hydrogen process, satisfies several of the principles of green chemistry. In this paper, four neutral half-sandwich complexes of Ru(II), Rh(III), and Ir(III) have been synthesized and tested as catalysts in the N-benzylation of amines with benzyl alcohol. The new derivatives contain a N^N′ anionic ligand derived from 5-(pyridin-2-ylmethylene)hydantoin (Hpyhy) that has never been tested in metal complexes with catalytic applications. In particular, the Ir derivatives, [(Cp*)IrX(pyhy)] (X = Cl or H), exhibit high activity along with good selectivity in the process. Indeed, the scope of the optimized protocol has been proved in the benzylation of several primary and secondary amines. The selectivity towards monoalkylated or dialkylated amines has been tuned by adjusting the amine:alcohol ratio and the reaction time. Experimental results support a mechanism consisting of three consecutive steps, two of which are Ir catalyzed, and a favorable condensation step without the assistance of the catalyst. Moreover, an unproductive competitive pathway can operate when the reaction is performed in open-air vessels, due to the irreversible release of H2. This route is hampered when the reaction is carried out in close vessels, likely because the release of H2 is reversed through metal-based heterolytic cleavage. From our viewpoint, these results show the potential of the new catalysts in a very attractive and promising methodology for the synthesis of amines.
- Ruiz-Casta?eda, Margarita,Rodríguez, Ana M.,Aboo, Ahmed H.,Manzano, Blanca R.,Espino, Gustavo,Xiao, Jianliang,Jalón, Félix A.
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- Phyllosilicate-derived Nickel-cobalt Bimetallic Nanoparticles for the Catalytic Hydrogenation of Imines, Oximes and N-heteroarenes
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The development of cost-effective, noble metal-free catalytic systems for the hydrogenation of unsaturated aliphatic, aromatic, and heterocyclic compounds is fundamental for future valorization of general feedstock. With this aim, we report here the preparation of highly dispersed bimetallic Ni/Co nanoparticles (NPs), by a one-pot deposition-precipitation of Ni and Co phases onto mesoporous SBA-15 silica. By adjusting the chemical composition in the starting mixture, three supported catalysts with different Ni to Co weight ratios were obtained, which were further subjected to treatments under reducing conditions at high temperatures. Characterization of the resulting solids evidenced a homogenous distribution of Ni and Co elements forming the NPs, the best results being obtained for Ni/Co-2 : 2 samples, for which 50 wt.percent Ni–50 wt.percent Co NPs are found located on the surface of the residual phyllosilicate. Ni/Co-2 : 2, presenting the best performances for the hydrogenation of 2-methyl-quinoline, was further evaluated in the catalytic hydrogenation of selected imines, oximes and N-heteroarenes. Due to the high dispersion of bimetallic Ni?Co NPs, excellent properties (activity and selectivity) in the conversion of the selected substrates are reported.
- Ciotonea, Carmen,Hammi, Nisrine,Dhainaut, Jérémy,Marinova, Maya,Ungureanu, Adrian,El Kadib, Abdelkrim,Michon, Christophe,Royer, Sébastien
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p. 4652 - 4663
(2020/08/19)
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- Asymmetric Synthesis of α-Aminoboronates via Rhodium-Catalyzed Enantioselective C(sp3)-H Borylation
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α-Aminoboronic acids, isostructural boron analogues of α-amino acids, have received much attention because of the important biomedical applications implicated for compounds containing this structure. Additionally, the inherent versatility of α-aminoboronic acids as synthetic intermediates through diverse carbon-boron bond transformations makes the efficient synthesis of these compounds highly desirable. Here, we present a Rh-monophosphite chiral catalytic system that enables a highly efficient enantioselective borylation of N-adjacent C(sp3)-H bonds for a range of substrate classes including 2-(N-alkylamino)heteroaryls and N-alkanoyl- or aroyl-based secondary or tertiary amides, some of which are pharmaceutical agents or related compounds. Various stereospecific transformations of the enantioenriched α-aminoboronates, including Suzuki-Miyaura coupling with aryl halides and the Rh-catalyzed reaction with an isocyanate derivative of α-amino acid, affording a new peptide chain elongation method, have been demonstrated. As a highlight of this work, the borylation protocol was successfully applied to the catalyst-controlled site-selective and stereoselective C(sp3)-H borylation of an unprotected dipeptidic compound, allowing remarkably streamlined synthesis of the anti-cancer drug molecule bortezomib and offering a straightforward route for the synthesis of privileged molecular architectures.
- Reyes, Ronald L.,Sato, Miyu,Iwai, Tomohiro,Sawamura, Masaya
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p. 589 - 597
(2020/01/22)
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- Enantioselective reduction of: N -alkyl ketimines with frustrated Lewis pair catalysis using chiral borenium ions
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Enantioselective reduction of ketimines was demonstrated using chiral N-heterocyclic carbene (NHC)-stabilised borenium ions in frustrated Lewis pair catalysis. High levels of enantioselectivity were achieved for substrates featuring secondary N-alkyl substituents. Comparative reactivity and mechanistic studies identify key determinants required to achieve useful enantioselectivity and represent a step forward in the further development of enantioselective FLP methodologies.
- Mercea, Dan M.,Howlett, Michael G.,Piascik, Adam D.,Scott, Daniel J.,Steven, Alan,Ashley, Andrew E.,Fuchter, Matthew J.
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p. 7077 - 7080
(2019/06/20)
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- Asymmetric Hydroboration of Heteroaryl Ketones by Aluminum Catalysis
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A series of methyl aluminum complexes bearing chiral biphenol-type ligands were found to be highly active catalysts in the asymmetric reduction of heterocyclic ketones (S/C = 100-500, ee up to 99%). The protocol is suitable for a wide range of substrates and has a high tolerance to functional groups. The formed 2-heterocyclic-alcohols are valuable building blocks in drug discovery or can be used as ligands in asymmetric catalysis. Isolation and comprehensive characterization of the reaction intermediates support a catalysis cycle proposed by DFT calculations.
- Lebedev, Yury,Polishchuk, Iuliia,Maity, Bholanath,Dinis Veloso Guerreiro, Miguel,Cavallo, Luigi,Rueping, Magnus
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supporting information
p. 19415 - 19423
(2019/12/24)
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- Catalyst-Free and Solvent-Free Facile Hydroboration of Imines
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A facile process for the catalyst-free and solvent-free hydroboration of aromatic as well as heteroaromatic imines is reported. This atom-economic methodology is scalable, compatible with sterically and electronically diverse imines, displaying excellent tolerance towards various functional groups, and works efficiently at ambient temperature in most of the cases, affording secondary amines in good to excellent yield after hydrolysis.
- Pandey, Vipin K.,Donthireddy, Siva Nagendra Reddy,Rit, Arnab
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p. 3255 - 3258
(2019/09/17)
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- A Highly Active PN3 Manganese Pincer Complex Performing N-Alkylation of Amines under Mild Conditions
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A highly active Mn(I) catalyst based on a nonsymmetric PN3-ligand scaffold for the N-alkylation of amines with alcohols utilizing the borrowing hydrogen methodology is reported. A broad range of anilines and the more challenging aliphatic amines were alkylated with primary and secondary alcohols. Moreover, the combination of low catalyst loadings and mild reaction conditions provides high efficiency for this atom-economic transformation.
- Homberg, Leonard,Roller, Alexander,Hultzsch, Kai C.
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supporting information
(2019/05/07)
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- Hydrogen-Borrowing Amination of Secondary Alcohols Promoted by a (Cyclopentadienone)iron Complex
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Thanks to a highly active catalyst, the scope of the (cyclopentadienone)iron complex-promoted 'hydrogen-borrowing' (HB) amination has been expanded to secondary alcohols, which had previously been reported to react only in the presence of large amounts of co-catalysts. A range of cyclic and acyclic secondary alcohols were reacted with aromatic and aliphatic amines giving fair to excellent yields of the substitution products. The catalyst was also able to promote the cyclization of diols bearing a secondary alcohol group with primary amines to generate saturated N-heterocycles.
- Aiolfi, Francesco,Bai, Xishan,Cettolin, Mattia,Dal Corso, Alberto,Gennari, Cesare,Piarulli, Umberto,Pignataro, Luca
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p. 3545 - 3555
(2019/09/09)
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- H2 Activation by Non-Transition-Metal Systems: Hydrogenation of Aldimines and Ketimines with LiN(SiMe3)2
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In recent years, H2 activation at non-transition-metal centers has met with increasing attention. Here, a system in which H2 is activated and transferred to aldimines and ketimines using substoichiometric amounts of lithium bis(trimethylsilyl)amide is reported. Notably, the reaction tolerates the presence of acidic protons in the α-position. Mechanistic investigations indicated that the reaction proceeds via a lithium hydride intermediate as the actual reductant.
- Elliott, Daniel C.,Marti, Alex,Mauleón, Pablo,Pfaltz, Andreas
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supporting information
p. 1918 - 1922
(2019/01/16)
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- Hitchhiker's Guide to Reductive Amination
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A comparative study of various widely used methods of reductive amination is reported. Specifically, such reducing agents as H 2, Pd/C, hydride reagents [NaBH 4, NaBH 3 CN, NaBH(OAc) 3 ], and CO/Rh 2 (OAc) 4 system were considered. For understanding the selectivity and activity of the reducing agents reviewed herein, different classes of starting materials were tested, including aliphatic and aromatic amines, as well as aliphatic and aromatic aldehydes and ketones. Most important advantages and drawbacks of the methods, such as selectivity of the target amine formation and toxicity of the reducing agents were compared. Methods were also considered from the viewpoint of green chemistry.
- Afanasyev, Oleg I.,Chusov, Denis,Makarova, Maria,Podyacheva, Evgeniya,Tsygankov, Alexey A.
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supporting information
p. 2667 - 2677
(2019/06/19)
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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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- Enantioselective Formation of 2-Azetidinones by Ring-Assisted Cyclization of Interlocked N-(α-Methyl)benzyl Fumaramides
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The synthesis of optically active interlocked and non-interlocked 2-azetidinones by intramolecular cyclization of N-(α-methyl)benzyl fumaramide [2]rotaxanes is described. Two different strategies of asymmetric induction were tested in which the chiral gro
- Martinez-Cuezva, Alberto,Bautista, Delia,Alajarin, Mateo,Berna, Jose
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supporting information
p. 6563 - 6567
(2018/05/03)
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- Metal Acetylide Elimination: The Key Step in the Cascade Decomposition and Transformation of Metalated Propargylamines
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Metal acetylide elimination facilitates a novel one-pot cascade metalation and elimination/addition route to a series of unsymmetrical secondary amines from the reaction of secondary propargylamines with organometallic reagents. Spectroscopic evidence suggests a dimetalated amido intermediate rather than an allene.
- Flynn, Matthew T.,Blair, Victoria L.,Andrews, Philip C.
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supporting information
p. 1225 - 1228
(2018/04/30)
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- Enhanced Catalytic Activity of Oxygen-Tethered IrIII NHC Complexes in Aqueous Transfer Hydrogenative Reductive Amination Reactions: Experimental Kinetic and Mechanistic Study
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The synthesis and characterization of seven new IrIII complexes containing o-phenoxide or o-naphthoxide chelated N-heterocyclic carbene ligands is reported herein. The crystal structures of six of the complexes have been determined. These complexes efficiently catalyze the transfer hydrogenative reductive amination (RA) of carbonyls and amines in water. Amongst the complexes tested, the introduction of o-naphthoxide on a nitrogen atom of imidazole based NHC ligand greatly increased the catalytic activity. The catalytic system has a broad substrate scope, which allows the synthesis of a variety of amines in excellent yields and with high turnover numbers up to 490 (for ketones) and 14800 (for aldehydes). The mechanism of aqueous RA reaction with an o-aryloxide chelated NHC-IrIII catalyst has been investigated by NMR spectroscopy and kinetic measurements. These studies suggest that the transfer hydrogenation (TH) is turnover-limited by the hydride formation step. As a result of the 1H NMR studies, the higher catalytic activity of o-naphthoxide chelated catalyst (3 g) over o-phenoxide chelated one (3 b) can be attributed partly due to the faster formation of an iridium hydride, the key intermediate in the RA reactions.
- ?zbozkurt, ?brahim Kayahan,Gülcemal, Derya,Günnaz, Salih,G?k?e, Ayta? Gürhan,?etinkaya, Bekir,Gülcemal, Süleyman
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p. 3593 - 3604
(2018/08/03)
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- A Bifunctional MOF Catalyst Containing Metal–Phosphine and Lewis Acidic Active Sites
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Post-synthetic modification of the hafnium metal–organic framework MOF-808(Hf) to include triarylphosphine ligands is reported. Sulfonated phenylphosphines are incorporated without oxidation to give a “MOF ligand” that can complex late transition metals such as Ir and Rh to give a bifunctional catalyst containing both metal–phosphine complexes and the Lewis acidic framework hafnium metal sites. The metallated phosphine-bearing MOFs act as fully heterogeneous bifunctional catalysts for tandem reductive amination and hydroaminomethylation reactions.
- Prasad, Ram R. R.,Dawson, Daniel M.,Cox, Paul A.,Ashbrook, Sharon E.,Wright, Paul A.,Clarke, Matthew L.
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supporting information
p. 15309 - 15318
(2018/09/27)
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- Iron-Catalyzed Reductive Amination of Aldehydes in Isopropyl Alcohol/Water Media as Hydrogen Sources
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Reductive amination can be carried in i-PrOH/H2O as hydrogen sources using commercially available iron carbonyl complexes. Within an aqueous alkaline environment, a hydridocarboferrate is formed and its reducing potential is exploited for hydrogenation of the imine (or iminium ion) obtained in situ from aldehydes or ketones, and primary or secondary amines in almost equimolar ratio. This completely sustainable and hydrogen-free process proceeds at 100 °C using Fe3(CO)12 as catalyst precursor under convectional heating while Fe2(CO)9 gave better results when the reaction was carried out under MW dielectric heating. Both enolizable and non-enolizable aldehydes may be successfully employed in reactions with aliphatic and aromatic amines. (Figure presented.).
- Petricci, Elena,Santillo, Niccolò,Castagnolo, Daniele,Cini, Elena,Taddei, Maurizio
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supporting information
p. 2560 - 2565
(2018/07/29)
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- Direct Reductive Amination of Carbonyl Compounds Catalyzed by a Moisture Tolerant Tin(IV) Lewis Acid
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Despite the ever-broadening applications of main-group ‘frustrated Lewis pair’ (FLP) chemistry to both new and established reactions, their typical intolerance of water, especially at elevated temperatures (>100 °C), represents a key barrier to their mainstream adoption. Herein we report that FLPs based on the Lewis acid iPr3SnOTf are moisture tolerant in the presence of moderately strong nitrogenous bases, even under high temperature regimes, allowing them to operate as simple and effective catalysts for the reductive amination of organic carbonyls, including for challenging bulky amine and carbonyl substrate partners. (Figure presented.).
- Sapsford, Joshua S.,Scott, Daniel J.,Allcock, Nathan J.,Fuchter, Matthew J.,Tighe, Christopher J.,Ashley, Andrew E.
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supporting information
p. 1066 - 1071
(2018/01/27)
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- Cobalt-Rhodium Heterobimetallic Nanoparticle-Catalyzed N-Alkylation of Amines with Alcohols to Secondary and Tertiary Amines
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Without the requirement for base or other additives, Co2Rh2/C can selectively catalyze both mono- and bis-N-alkylation through the coupling of simple alcohols with amines, yielding a range of secondary and tertiary amines in good to excellent isolated yields. The reaction can be applied to benzyl alcohol with optically active 1-phenylethan-1-amines, and secondary amines were isolated in quantitative yields with an excellent enantiomeric excess (ee > 94%). Selectivity is achieved by varying the reaction temperature and amount of catalyst used. This catalytic system has several advantages including eco-friendliness and a simple workup procedure. The catalyst can be successfully recovered and reused ten times without any significant loss of activity.
- Chung, Hyunho,Chung, Young Keun
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p. 8533 - 8542
(2018/07/30)
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- A Tethered Ru–S Complex with an Axial Chiral Thiolate Ligand for Cooperative Si–H Bond Activation: Application to Enantioselective Imine Reduction
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An axial chiral version of the 2,6-dimesitylphenyl group attached to sulfur is reported. Its multistep preparation starts from (S)-binol, and the thiol group is established by a racemization-free thermal Newman–Kwart rearrangement. The new chiral thiolate ligand decorated with one mesityl group is used in the synthesis of a tethered ruthenium chloride complex. Its spectroscopic characterization revealed solvent-dependent epimerization at the ruthenium center. The major diastereomer is crystallographically characterized. Chloride abstraction with tetrakis[3,5-bis(trifluoromethyl)phenyl]borate (NaBArF4) yields the corresponding coordinatively unsaturated ruthenium complex with the Ru?S bond exposed. Si?H bond activation at this Ru?S bond proceeds in syn fashion but with moderate facial selectivity (d.r.=70:30), generating diastereomeric chiral-at-ruthenium hydrosilane adducts. Their application to catalytic imine hydrosilylation led to promising enantioinduction (40 % ee), thereby providing proof of concept for asymmetric catalysis involving cooperative Si?H bond activation.
- Wübbolt, Simon,Maji, Modhu Sudan,Irran, Elisabeth,Oestreich, Martin
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supporting information
p. 6213 - 6219
(2017/05/08)
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- MOF-derived cobalt nanoparticles catalyze a general synthesis of amines
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The development of base metal catalysts for the synthesis of pharmaceutically relevant compounds remains an important goal of chemical research. Here, we report that cobalt nanoparticles encapsulated by a graphitic shell are broadly effective reductive amination catalysts. Their convenient and practical preparation entailed template assembly of cobaltdiamine- dicarboxylic acid metal organic frameworks on carbon and subsequent pyrolysis under inert atmosphere.The resulting stable and reusable catalysts were active for synthesis of primary, secondary, tertiary, and N-methylamines (more than 140 examples).The reaction couples easily accessible carbonyl compounds (aldehydes and ketones) with ammonia, amines, or nitro compounds, and molecular hydrogen under industrially viable and scalable conditions, offering cost-effective access to numerous amines, amino acid derivatives, and more complex drug targets.
- Jagadeesh, Rajenahally V.,Murugesan, Kathiravan,Alshammari, Ahmad S.,Neumann, Helfried,Pohl, Marga-Martina,Radnik, J?rg,Beller, Matthias
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p. 326 - 332
(2017/09/28)
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- Expanding the Boundaries of Water-Tolerant Frustrated Lewis Pair Hydrogenation: Enhanced Back Strain in the Lewis Acid Enables the Reductive Amination of Carbonyls
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The development of a boron/nitrogen-centered frustrated Lewis pair (FLP) with remarkably high water tolerance is presented. As systematic steric tuning of the boron-based Lewis acid (LA) component revealed, the enhanced back-strain makes water binding increasingly reversible in the presence of relatively strong base. This advance allows the limits of FLP's hydrogenation to be expanded, as demonstrated by the FLP reductive amination of carbonyls. This metal-free catalytic variant displays a notably broad chemoselectivity and generality.
- Dorkó, éva,Szabó, Márk,Kótai, Bianka,Pápai, Imre,Domján, Attila,Soós, Tibor
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supporting information
p. 9512 - 9516
(2017/08/01)
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- BArF3-Catalyzed Imine Hydroboration with Pinacolborane Not Requiring the Assistance of an Additional Lewis Base
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The rarely used boron Lewis acid tris[3,5-bis(trifluoromethyl)phenyl]borane (BArF3) is found to be an excellent catalyst for metal-free hydroboration of imines. In the presence of 1.0 mol % of BArF3, several ketimines and aldimines undergo hydroboration with pinacolborane (HBpin) at room temperature without the aid of an external Lewis base. BArF3 is more reactive than other Lewis acidic boranes, including the often-used tris(pentafluorophenyl)borane (B(C6F5)3). The steric hindrance imparted by the six fluorine atoms ortho to the boron center in B(C6F5)3 accounts for this. Mechanistic control experiments indicate conventional Lewis acid catalysis involving imine activation and hydride transfer from HBpin.
- Yin, Qin,Soltani, Yashar,Melen, Rebecca L.,Oestreich, Martin
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p. 2381 - 2384
(2017/07/17)
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- Hydroboration Catalyzed by 1,2,4,3-Triazaphospholenes
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The synthesis and study of the catalytic activity of 1,2,4,3-triazaphospholenes (TAPs) is reported. TAPs represent a more modular scaffold than previously reported diazaphospholenes. TAP halides were shown to catalyze the 1,2 hydroboration of 19 imines, and three α,β unsaturated aldehydes with pinacolborane, including examples that did not undergo hydroboration by previously reported diazaphospholene systems. DFT calculations support a mechanism where a triazaphospholene cation interacts with the substrate, a mechanism distinct from diazaphospholene catalyzed hydroborations.
- Tien, Chieh-Hung,Adams, Matt R.,Ferguson, Michael J.,Johnson, Erin R.,Speed, Alexander W. H.
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supporting information
p. 5565 - 5568
(2017/10/25)
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- Water-Soluble Iridium N-Heterocyclic Carbene Complexes for the Alkylation of Amines with Alcohols
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A new series of water-soluble Ir complexes with N-heterocyclic carbene ligands that bear ester and amide groups has been obtained and fully characterized. The new complexes are highly reactive and selective for the alkylation of amines with alcohols with a 1:1 ratio of reactants in water and in the absence of base or other additives. The catalytic system has a broad substrate scope, which allows the synthesis of a variety of primary and secondary amines in excellent yields. A tolerance to a large range of functional groups was obtained.
- Fernandes, Ana,Royo, Beatriz
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p. 3912 - 3917
(2017/09/28)
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- Diazaphospholene Precatalysts for Imine and Conjugate Reductions
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The first examples of 1,3,2-diazaphospholene-catalyzed imine reduction and conjugate reduction reactions are reported. This approach employs readily synthesized alkoxydiazaphospholene precatalysts that can be handled in open air. Reduction of substrates containing Lewis basic functionality, isolated unsaturation, and protic functional groups was accomplished. The synthetic utility of this approach is demonstrated by the synthesis of the important antiparkinson medicine rasagiline and the natural product zingerone.
- Adams, Matt R.,Tien, Chieh-Hung,Huchenski, Blake S. N.,Ferguson, Michael J.,Speed, Alexander W. H.
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supporting information
p. 6268 - 6271
(2017/05/19)
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- Simple Metal-Free Direct Reductive Amination Using Hydrosilatrane to Form Secondary and Tertiary Amines
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This work describes the use of cheap, safe, and easy-to-handle hydrosilatrane as the reductant in direct reductive amination reactions. This efficient method enables a facile, metal-free access to secondary and tertiary amines from a wide range of aldehydes and ketones, with the synthesis of tertiary amines requiring no additives at all. This reaction demonstrates excellent functional group tolerance, chemoselectivity, and scalability. (Figure presented.).
- Varjosaari, Sami E.,Skrypai, Vladislav,Suating, Paolo,Hurley, Joseph J. M.,Lio, Ashley M. De,Gilbert, Thomas M.,Adler, Marc J.
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supporting information
p. 1872 - 1878
(2017/06/09)
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- Expanding Water/Base Tolerant Frustrated Lewis Pair Chemistry to Alkylamines Enables Broad Scope Reductive Aminations
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Lower Lewis acidity boranes demonstrate greater tolerance to combinations of water/strong Br?nsted bases than B(C6F5)3, this enables Si?H bond activation by a frustrated Lewis pair (FLP) mechanism to proceed in the presence of H2O/alkylamines. Specifically, BPh3has improved water tolerance in the presence of alkylamines as the Br?nsted acidic adduct H2O–BPh3does not undergo irreversible deprotonation with aliphatic amines in contrast to H2O–B(C6F5)3. Therefore BPh3is a catalyst for the reductive amination of aldehydes and ketones with alkylamines using silanes as reductants. A range of amines inaccessible using B(C6F5)3as catalyst, were accessible by reductive amination catalysed by BPh3via an operationally simple methodology requiring no purification of BPh3or reagents/solvent. BPh3has a complementary reductive amination scope to B(C6F5)3with the former not an effective catalyst for the reductive amination of arylamines, while the latter is not an effective catalyst for the reductive amination of alkylamines. This disparity is due to the different pKavalues of the water–borane adducts and the greater susceptibility of BPh3species towards protodeboronation. An understanding of the deactivation processes occurring using B(C6F5)3and BPh3as reductive amination catalysts led to the identification of a third triarylborane, B(3,5-Cl2C6H3)3, that has a broader substrate scope being able to catalyse the reductive amination of both aryl and alkyl amines with carbonyls.
- Fasano, Valerio,Ingleson, Michael J.
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supporting information
p. 2217 - 2224
(2017/02/18)
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- REACTIONS OF STANNYL CATIONS
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The present invention relates to a method of reducing, cleaving and/or coupling at least one C=O, C-O, C=C or C=N bond of a compound, using a reagent comprising a stannyl cation.
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-
Page/Page column 22; 23
(2018/01/17)
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- Asymmetric Transfer Hydrogenation of Imines using Alcohol: Efficiency and Selectivity are Influenced by the Hydrogen Donor
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The influence of the alcohol, as the hydrogen donor, on the efficiency and selectivity of the asymmetric transfer hydrogenation (ATH) of imines is reported for the first time. This discovery not only leads to a highly enantioselective access to N-aryl and N-alkyl amines, but also provides new insight into the mechanism of the ATH of imines. Both experimental and computational studies provide support for the reaction pathway involving an iridium alkoxide as the reducing species.
- Pan, Hui-Jie,Zhang, Yao,Shan, Chunhui,Yu, Zhaoyuan,Lan, Yu,Zhao, Yu
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supporting information
p. 9615 - 9619
(2016/08/10)
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- Heterogeneous Catalytic Reductive Amination of Carbonyl Compounds with Ni-Al Alloy in Water as Solvent and Hydrogen Source
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The heterogeneous catalytic reductive amination of carbonyl compounds has been achieved by reactions of ammonium hydroxide and various amines with ketones and aldehydes. The process is based on the application of Raney type Ni-Al alloy in an aqueous medium. The reaction of the carbonyl compounds with the amine provided the corresponding Schiff bases that immediately underwent a reduction to provide primary and secondary amines as products. The controlled reaction of the Al content of the alloy with the solvent water generates hydrogen, and the in situ formed Raney Ni serves as a hydrogenation catalyst. The method is a simple and efficient way of preparing a broad variety of primary and secondary amines.
- Sch?fer, Christian,Ni?anci, Bilal,Bere, Matthew P.,Da?tan, Arif,T?r?k, Béla
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p. 3127 - 3133
(2016/09/09)
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- Iridium(I) Complexes Bearing a Noninnocent PNP-Pincer-Type Phosphaalkene Ligand: Catalytic Application in the Base-Free N-Alkylation of Amines with Alcohols
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A series of IrI complexes [Ir(L)(PPEP?)] [L = Cl- (3), CO (4), tBuNC (5), PMe3 (6), PPh3 (7)], coordinated with a PNP-pincer-type phosphaalkene ligand bearing a dearomatized pyridine ring (PPEP?), have been prepared and their catalytic properties for the dehydration/condensation of amines with alcohols has been examined. The catalytic reactions successfully proceed under base-free conditions to give N-alkylated amines and their dehydrogenation derivatives (imines). The product selectivity is dependent on L coordinated with Ir(PPEP?). Complexes 4 and 5 that contain π-accepting ligands (CO, tBuNC) form N-alkylated amines as the major products in a closed system using a nitrogen-gas-filled Schlenk tube. In contrast, complex 7 that contain PPh3 as L produces imines as the major products under a nitrogen-gas flow. The reason for the selectivity change depending on L is discussed based on stoichiometric reactions using model compounds of presumed catalytic intermediates. PNP-pincer-type phosphaalkene complexes of IrI bearing a dearomatized pyridine ring have been found to catalyze the dehydration/condensation of amines with alcohols under base-free conditions to afford N-alkylated amines and imines in high yields. The product selectivity can be controlled by the choice of auxiliary ligands (L) as well as the reaction conditions.
- Chang, Yung-Hung,Tanigawa, Ippei,Taguchi, Hiro-Omi,Takeuchi, Katsuhiko,Ozawa, Fumiyuki
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p. 754 - 760
(2016/03/01)
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- The kinetics and mechanism of the organo-iridium catalysed racemisation of amines
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The dimeric iodo-iridium complex [IrCp?I2]2 (Cp? = pentamethylcyclopentadiene) is an efficient catalyst for the racemisation of secondary and tertiary amines at ambient and higher temperatures with a low catalyst loading. The racemisation occurs with pseudo-first-order kinetics and the corresponding four rate constants were obtained by monitoring the time dependence of the concentrations of the (R) and (S) enantiomers starting with either pure (R) or (S) and show a first-order dependence on catalyst concentration. Low temperature 1H NMR data is consistent with the formation of a 1 : 1 complex with the amine coordinated to the iridium and with both iodide anions still bound to the metal-ion, but at the higher temperatures used for kinetic studies binding is weak and so no saturation zero-order kinetics are observed. A cross-over experiment with isotopically labelled amines demonstrates the intermediate formation of an imine which can dissociate from the iridium complex. Replacing the iodides in the catalyst by other ligands or having an amide substituent in Cp? results in a much less effective catalysts for the racemisation of amines. The rate constants for a deuterated amine yield a significant primary kinetic isotope effect kH/kD = 3.24 indicating that hydride transfer is involved in the rate-limiting step.
- Stirling, Matthew J.,Mwansa, Joseph M.,Sweeney, Gemma,Blacker, A. John,Page, Michael I.
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p. 7092 - 7098
(2016/07/30)
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- Cationic Iridium and Rhodium Complexes with C-N Chelating Primary Benzylic Amine Ligands as Potent Catalysts for Hydrogenation of Unsaturated Carbon-Nitrogen Bonds
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Cationic half-sandwich C-N chelating Ir and Rh complexes [Cp?M(NCCH3){2(N,C)-NH2CR2-2-C6H4}]+SbF6- (1a, M = Ir, R = CH3; 1b, M = Ir, R = C6H5; 2a, M = Rh, R = CH3; 2b, M = Rh, R = C6H5) are synthesized by AgSbF6-mediated halide abstraction from neutral azametallacycles derived from tritylamine or cumylamine and are fully characterized by NMR spectroscopy and X-ray crystallography. The treatment of the cationic complex 1b with H2 gas under ambient conditions in the presence of triethylamine in THF-d8 quantitatively yielded hydrido(amine) complex [Cp?Ir(H){2(N,C)-NH2C(C6H5)2-2-C6H4}] (4). The C-N chelating Ir complex shows a higher catalytic activity than an N-N chelating complex, [Cp?Ir(NCCH3)(Tscydn)]+SbF6- (3; Tscydn = N-(p-toluenesulfonyl)-1,2-cyclohexanediamime), that has been previously used for the asymmetric hydrogenation of acyclic imines. For example, the cationic Ir complex 1a promoted the hydrogenation of N-(1-phenylethylidene)benzylamine under 30 atm at 30 °C in the presence of excess AgSbF6 to produce the corresponding amine in 97% yield within 2 h. The cationic Rh complexes 2 serve as efficient catalysts for hydrogenative condensation of nitriles in the presence of AgSbF6, producing dibenzylamines selectively even at 60 °C.
- Sato, Yasuhiro,Kayaki, Yoshihito,Ikariya, Takao
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p. 1257 - 1264
(2016/06/01)
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- Iron-catalyzed transfer hydrogenation of imines assisted by an iron-based Lewis acid
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An iron-catalyzed transfer hydrogenation of N-aryl and N-alkyl imines using isopropanol as the hydrogen donor is reported for the first time. A combination of two iron complexes serving different roles is the key for the success of this catalytic system. As a result, an environmentally friendly and precious metal-free transfer hydrogenation of imines has been developed. The use of a suitable co-catalyst as an activator not only led to efficient transfer hydrogenation, but also showed potential in enantioselective transformation.
- Pan, Hui-Jie,Ng, Teng Wei,Zhao, Yu
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supporting information
p. 5490 - 5493
(2016/07/06)
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- Synthesis and catalytic reactivity of bis(amino)cyclopropenylidene carbene-borane adducts
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The first reported neutral boron(III) adducts of bis(amino)cyclopropenylidene carbenes (BAC carbenes) have been synthesized, structurally characterized, and applied in homogeneous reaction chemistry. These air-stable adducts have been prepared by the combination of a BAC carbene lithium tetrafluoroborate adduct with borane dimethyl sulfide, boron trifluoride etherate, or dicyclohexylborane. A borenium cation derived in situ from the dicyclohexylborane adduct catalytically reduces unhindered benzyl ketimines, a class of substrate that cannot be reduced by prior borenium catalysts, at room temperature, employing 20 atm of hydrogen gas as the terminal reductant.
- Huchenski, Blake S. N.,Adams, Matt R.,McDonald, Robert,Ferguson, Michael J.,Speed, Alexander W. H.
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supporting information
p. 3101 - 3104
(2016/10/09)
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- L-Valine derived chiral N-sulfinamides as effective organocatalysts for the asymmetric hydrosilylation of N-alkyl and N-aryl protected ketimines
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l-Valine derived N-sulfinamides have been developed as efficient enantioselective Lewis basic organocatalysts for the asymmetric reduction of N-aryl and N-alkyl ketimines with trichlorosilane. Catalyst 3c afforded up to 99% yield and 96% ee in the reduction of N-alkyl ketimines and up to 98% yield and 98% ee in the reduction of N-aryl ketimines.
- Wang, Chao,Wu, Xinjun,Zhou, Li,Sun, Jian
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p. 577 - 582
(2015/02/02)
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- Chiral molecular tweezers: Synthesis and reactivity in asymmetric hydrogenation
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We report the synthesis and reactivity of a chiral aminoborane displaying both rapid and reversible H2 activation. The catalyst shows exceptional reactivity in asymmetric hydrogenation of enamines and unhindered imines with stereoselectivities of up to 99% ee. DFT analysis of the reaction mechanism pointed to the importance of both repulsive steric and stabilizing intermolecular non-covalent forces in the stereodetermining hydride transfer step of the catalytic cycle.
- Lindqvist, Markus,Borre, Katja,Axenov, Kirill,Kótai, Bianka,Nieger, Martin,Leskel?, Markku,Pápai, Imre,Repo, Timo
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supporting information
p. 4038 - 4041
(2015/04/14)
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- Graphene-supported NiPd alloy nanoparticles: A novel and highly efficient heterogeneous catalyst system for the reductive amination of aldehydes
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A novel and highly efficient heterogeneous catalytic reductive amination of aldehydes is described. The recently developed graphene supported NiPd alloy nanoparticle (G-NiPd) catalyst using ammonia borane (AB) as a green, stable and safe hydrogen donor was used in a water/methanol mixture (v/v = 2/3) under ambient conditions. The catalytic system was successfully applied in the reductive amination of various substituted aldehydes with amines and the corresponding products were obtained in (up to) 99% yield in 6 h. The G-NiPd catalyst could be recycled up to five times without any significant loss in the product yield.
- Ni?anci, Bilal,Ganjehyan, Khadijeh,Metin, ?nder,Da?tan, Arif,T?r?k, Béla
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p. 191 - 197
(2015/09/22)
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