- Zirconium-hydride-catalyzed site-selective hydroboration of amides for the synthesis of amines: Mechanism, scope, and application
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Developing mild and efficient catalytic methods for the selective synthesis of amines is a longstanding research objective. In this respect, catalytic deoxygenative amide reduction has proven to be promising but challenging, as this approach necessitates selective C–O bond cleavage. Herein, we report the selective hydroboration of primary, secondary, and tertiary amides at room temperature catalyzed by an earth-abundant-metal catalyst, Zr-H, for accessing diverse amines. Various readily reducible functional groups, such as esters, alkynes, and alkenes, were well tolerated. Furthermore, the methodology was extended to the synthesis of bio- and drug-derived amines. Detailed mechanistic studies revealed a reaction pathway entailing aldehyde and amido complex formation via an unusual C–N bond cleavage-reformation process, followed by C–O bond cleavage.
- Han, Bo,Jiao, Haijun,Wu, Lipeng,Zhang, Jiong
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p. 2059 - 2067
(2021/09/02)
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- Ruthenium-Catalyzed Methylation of Amines with Paraformaldehyde in Water under Mild Conditions
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Methylated amines are highly important for a variety of pharmaceutical and agrochemical applications. Existing routes for their formation result in the production of large amounts of waste or require high reaction temperatures, both of which impact the ecological and economical footprint of the methodologies. Herein, we report the ruthenium-catalyzed reductive methylation of a range of aliphatic amines, using paraformaldehyde as both substrate and hydrogen source, in combination with water. This reaction proceeds under mild aqueous reaction conditions. Additionally the use of a secondary phase for catalyst retention and recycling has been investigated with promising results.
- van der Waals, Dominic,Heim, Leo. E.,Gedig, Christian,Herbrik, Fabian,Vallazza, Simona,Prechtl, Martin H. G.
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p. 2343 - 2347
(2016/10/24)
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- Supramolecular Ga4L612- cage photosensitizes 1,3-rearrangement of encapsulated guest via photoinduced electron transfer
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The K12Ga4L6 supramolecular cage is photoactive and enables an unprecedented photoreaction not observed in bulk solution. Ga4L612- cages photosensitize the 1,3-rearrangement of encapsulated cinnamylammonium cation guests from the linear isomer to the higher energy branched isomer when irradiated with UVA light. The rearrangement requires light and guest encapsulation to occur. The Ga4L612- cage-mediated reaction mechanism was investigated by UV/vis absorption, fluorescence, ultrafast transient absorption, and electrochemical experiments. The results support a photoinduced electron transfer mechanism for the 1,3-rearrangement, in which the Ga4L612- cage absorbs photons and transfers an electron to the encapsulated cinnamylammonium ion, which undergoes C-N bond cleavage, followed by back electron transfer to the cage and recombination of the guest fragments to form the higher energy isomer.
- Dalton, Derek M.,Ellis, Scott R.,Nichols, Eva M.,Mathies, Richard A.,Dean Toste,Bergman, Robert G.,Raymond, Kenneth N.
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supporting information
p. 10128 - 10131
(2015/09/01)
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- Development and mechanistic investigation of a highly efficient iridium(V) silyl complex for the reduction of tertiary amides to amines
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The cationic Ir(III) acetone complex (POCOP)Ir(H)2(acetone) + (POCOP = 2,6-bis(di-tert-butylphosphinito)phenyl) was shown to catalyze the reduction of a variety of tertiary amides to amines using diethylsilane as reductant. Mechanistic studies established that a minor species generated in the reaction, the neutral silyl trihydride Ir(V) complex (POCOP)IrH3(SiEt2H), was the catalytically active species. High concentrations of this species could be conveniently generated by treatment of readily available (POCOP)IrHCl with tert-butoxide in the presence of Et2SiH2 under H2. Thus, using this mixture in the presence of a trialkylammonium salt, a wide array of tertiary amides, including extremely bulky substrates, are rapidly and quantitatively reduced to tertiary amines under mild conditions with low catalyst loading. A detailed mechanistic study has been carried out and intermediates identified. In brief, (POCOP)IrH3(SiEt2H) reduces the amide to the hemiaminal silyl ether that, in the presence of a trialkylammonium salt, is ionized to the iminium ion, which is then reduced to the tertiary amine by Et 2SiH2. Good functional group compatibility is demonstrated, and a high catalyst stability has provided turnover numbers as high as 10 000.
- Park, Sehoon,Brookhart, Maurice
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experimental part
p. 640 - 653
(2012/03/13)
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- Spiroborate catalyzed reductions with N,N-diethylaniline borane
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Reduction of esters, amides, and ketones by N,N-diethylaniline borane is accelerated by catalysts derived from spiroborate complexes. Esters are reduced at ambient temperature in less than 4 h with this amine borane and 5 mol % spiroborate 6. Functional group selectivity shows ketone and tertiary amide reduction is faster than ester or nitrile reduction.
- Coleridge, Brian M.,Angert, Thomas P.,Marks, Lucas R.,Hamilton, Patrick N.,Sutton, Christopher P.,Matos, Karl,Burkhardt, Elizabeth R.
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supporting information; experimental part
p. 5973 - 5976
(2010/11/21)
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- An efficient metal-free reduction using diphenylsilane with (tris-perfluorophenyl)borane as catalyst
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An efficient metal-free reduction of various C{double bond, long}X (X = O, N, C) bonds into their corresponding amines or hydrocarbons using the Ph2SiH2/B(C6F5)3 catalytic system is demonstrated. This protocol reduces enamines, enol esters, carbonyls, amides, and isocyanates.
- Tan, MeiXuan,Zhang, Yugen
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supporting information; experimental part
p. 4912 - 4915
(2009/12/01)
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- Aminomethylation of organic halides promoted by zinc in protic medium
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Organic halides undergo smooth aminomethylation by secondary amines and aqueous formaldehyde promoted by metallic zinc under copper(I) catalysis. Good to excellent yields are obtained with primary, secondary, and tertiary iodides, allylic, propargylic, and benzylic bromides and with α-bromoesters. In most cases, DMSO is the best solvent, but dioxane is preferable for some more reactive halides. Additional experiments with radical quenchers and promoters and the use of 'radical clocks' indicate a stepwise reaction mechanism initiated by the attack of an alkyl radical to iminium ion.
- Estevam, Idália H. S.,Da Silva, Margarete F.,Bieber, Lothar W.
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p. 7601 - 7604
(2007/10/03)
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- A novel aminomethylation reaction of gaseous alkanes with tert-methylamine N-oxides via C-H bond activation by copper(II) salts
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The Cu(OAc)2/CF3COOH (TFA) system catalyzes the aminomethylation of gaseous alkanes such as propane and ethane with trimethylamine N-oxide to give N,N-dimethylisobutylamine (1) and N,N-dimethylpropylamine (7), respectively.The corresponding trifluoroacetates are also formed as by-products from the reactions of methane and propane. Keywords: Copper acetate; Aminomethylation; Amine N-oxide; C-H bond activation; C-C bond formation; Alkane
- Taniguchi, Yuki,Horie, Shiro,Takaki, Ken,Fujiwara, Yuzo
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p. 137 - 142
(2007/10/03)
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- Ion-Dipole Complexes in the Unimolecular Reactions of Isolated Organic Ions. Effect of N-Methylation on Olefin and Amine Loss from Protonated Aliphatic Amines
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The slow unimolecular fragmentation reactions os 18 gaseous protonated aliphatic amines of general formula R1NH(1+)R2R3 (R1=Prn, Pri, Bun, Bui, Bus, or But; R2,R3=H,CH3) are reported and discussed.Two decomposition routes are observed for a metastable ions R1NH(1+)R2R3.The first involves elimination of a neutral amine, R2R3NH, and formation of a carbocation, R1(1+), via a mechanism involving an incipient cation bound to the developing amine by an ion-dipole attraction.Rearrangement of the cation, to give thermodynamically more stable isomers, is feasible in these ion-dipole complexes.Further reorganization of the complexes leads to a species in which an incipient olefin 1-H> and an amine 2R3NH> are co-ordinated to a common proton.Dissociation of these proton-bound complexes, with retention of the proton by the developing amine, results in olefin loss, which is the secondreaction undergone by metastable ions R1NH(1+)R2R3.The relative abundance of amine expulsion is greater for protonated amines containing a primary alkyl group, R1, than is the case for isomeric ions containing secondary or tertiary alkyl groups.Progressive methylation of the nitrogen atom decreases the relative abundance of amine loss from R1NH(1+)R2R3, regardless of the nature of the principal alkyl group.These two trends are explained in terms of the energetics of the intermediates and products involved in the decomposition of the protonated amines.
- Bowen, Richard D.,Harrison, Alex G.,Reiner, Eric J.
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p. 1009 - 1014
(2007/10/02)
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- Mechanism of Elimination Reactions. 38. Why Is the Effect of Successive β-Alkyl Substitution on the Rates of Elimination from Quaternary Ammonium Salts Nonadditive?
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Possible reasons are examined for the nonadditivity of the effect of successive β-methyl substitution on the rates of elimination reactions of quaternary ammonium salts.The temperature dependences of the deuterium isotope effects in E2 reactions of R1R2NMe2+ show that tunneling is not a significant source of nonadditivity.Neither is a change of gross mechanism or stereochemistry, for studies with C4H9CHDCHDNMe3+ and C4H9(CH3)CHCHDNMe3+ show the reactions to be very predominantly (>88percent) anti-E2 in both cases.Secondary tritium isotope effects with R1R2CHCHTNMe3+ increase, however in the order ethyl (1.108 +/- 0.002), propyl (1.150 +/- 0.015), isobutyl (1.216 +/- 0.012).This result suggests increasing rehybridization at the α-carbon in the transition state and therefore a shift toward less E1cB and more central-E2 character.Since methyl substitution is expected to favor a developing double bond, the much smaller rate-depressing effect of the second β-methyl is accounted for by such a shift in transition-state character.
- Wu, Shune-Long,Tao, Yu-Tai,Saunders, William H.
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p. 7583 - 7588
(2007/10/02)
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