- α-Effect Menschutkin alkylations
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The Menschutkin-type alkylation of substituted N-methylanilines with methyl arenesulfonates is compared to the same reaction with substituted N- phenylhydroxylamines. The α-effects are small but measurable. The Hammett ρ parameters are not useful in this reaction series as an index of transition- state character. The use of β(1g)(Me) parameters along with β(nuc) values allows the transition states to be placed on the energy surface. The pattern is that the α-nucleophiles form tighter transition states than the normal nucleophiles. The size of the α-effect is related to the ionization potentials (IPs) computed by the AM1 Hamiltonian for a wide variety of reactions showing the α-effect. The larger α-effects depend more greatly on the IP.
- Fountain,Hutchinson,Mulhearn,Yu Bo Xu
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Read Online
- Light-Promoted C–N Coupling of Aryl Halides with Nitroarenes
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A photochemical C–N coupling of aryl halides with nitroarenes is demonstrated for the first time. Catalyzed by a NiII complex in the absence of any external photosensitizer, readily available nitroarenes undergo coupling with a variety of aryl halides, providing a step-economic extension to the widely used Buchwald–Hartwig C–N coupling reaction. The method tolerates coupling partners with steric-congestion and functional groups sensitive to bases and nucleophiles. Mechanistic studies suggest that the reaction proceeds via the addition of an aryl radical, generated from a NiI/NiIII cycle, to a nitrosoarene intermediate.
- Li, Gang,Yang, Liu,Liu, Jian-Jun,Zhang, Wei,Cao, Rui,Wang, Chao,Zhang, Zunting,Xiao, Jianliang,Xue, Dong
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supporting information
p. 5230 - 5234
(2021/02/05)
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- Polyfunctionalized biaryls accessed by a one-pot nucleophilic aromatic substitution and sigmatropic rearrangement reaction cascade under mild conditions
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A practical synthetic method has been developed for polyfunctionalized biaryls based on a facile one-pot nucleophilic aromatic substitution (SNAr) reaction and [5,5]- or [3,3]-sigmatropic rearrangement reaction cascade. Under mild basic conditions, N-arylhydroxylamines reacted with o-activated fluoro (het)arenes to form N,O-diarylhydroxylamine intermediates which underwent spontaneously selective [5,5]-sigmatropic rearrangement reaction to produce diverse functionalized 4-amino-4′-hydroxy-1,1′-biaryls. A sequential SNAr reaction and [3,3]-sigmatropic rearrangement took place between N-arylhydroxylamines and 2-fluoropyridine derivatives or 4-fluorobenzonitrile to afford functionalized 2-amino-2′-hydroxy-1,1′-biaryls. As invaluable and unique building blocks, the resulting biaryls were applied in the straightforward synthesis of N2,O2-coronarene, carbazole, aza- and diaza carbazole derivatives.
- Liang, Dong-Dong,Guo, Shen-Yi,Tong, Shuo,Wang, Mei-Xiang
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supporting information
(2021/02/09)
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- Selective Reduction of Nitroarenes to Arylamines by the Cooperative Action of Methylhydrazine and a Tris(N-heterocyclic thioamidate) Cobalt(III) Complex
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We report an efficient catalytic protocol that chemoselectively reduces nitroarenes to arylamines, by using methylhydrazine as a reducing agent in combination with the easily synthesized and robust catalyst tris(N-heterocyclic thioamidate) Co(III) complex [Co(κS,N-tfmp2S)3], tfmp2S = 4-(trifluoromethyl)-pyrimidine-2-thiolate. A series of arylamines and heterocyclic amines were formed in excellent yields and chemoselectivity. High conversion yields of nitroarenes into the corresponding amines were observed by using polar protic solvents, such as MeOH and iPrOH. Among several hydrogen donors that were examined, methylhydrazine demonstrated the best performance. Preliminary mechanistic investigations, supported by UV-vis and NMR spectroscopy, cyclic voltammetry, and high-resolution mass spectrometry, suggest a cooperative action of methylhydrazine and [Co(κS,N-tfmp2S)3] via a coordination activation pathway that leads to the formation of a reduced cobalt species, responsible for the catalytic transformation. In general, the corresponding N-arylhydroxylamines were identified as the sole intermediates. Nevertheless, the corresponding nitrosoarenes can also be formed as intermediates, which, however, are rapidly transformed into the desired arylamines in the presence of methylhydrazine through a noncatalytic path. On the basis of the observed high chemoselectivity and yields, and the fast and clean reaction processes, the present catalytic system [Co(κS,N-tfmp2S)3]/MeNHNH2 shows promise for the efficient synthesis of aromatic amines that could find various industrial applications.
- Ioannou, Dimitris I.,Gioftsidou, Dimitra K.,Tsina, Vasiliki E.,Kallitsakis, Michael G.,Hatzidimitriou, Antonios G.,Terzidis, Michael A.,Angaridis, Panagiotis A.,Lykakis, Ioannis N.
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supporting information
p. 2895 - 2906
(2021/02/27)
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- Selective Photoinduced Reduction of Nitroarenes to N-Arylhydroxylamines
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We report the selective photoinduced reduction of nitroarenes to N-arylhydroxylamines. The present methodology facilitates this transformation in the absence of catalyst or additives and uses only light and methylhydrazine. This noncatalytic photoinduced transformation proceeds with a broad scope, excellent functional-group tolerance, and high yields. The potential of this protocol reflects on the selective and straightforward conversion of two general antibiotics, azomycin and chloramphenicol, to the bioactive hydroxylamine species.
- Kallitsakis, Michael G.,Ioannou, Dimitris I.,Terzidis, Michael A.,Kostakis, George E.,Lykakis, Ioannis N.
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supporting information
p. 4339 - 4343
(2020/06/08)
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- Tandem selective reduction of nitroarenes catalyzed by palladium nanoclusters
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We report a catalytic tandem reduction of nitroarenes by sodium borohydride (NaBH4) in aqueous solution under ambient conditions, which can selectively produce five categories of nitrogen-containing compounds: anilines, N-aryl hydroxylamines, azoxy-, azo- and hydrazo-compounds. The catalyst is in situ-generated ultrasmall palladium nanoclusters (Pd NCs, diameter of 1.3 ± 0.3 nm) from the reduction of Pd(OAc)2 by NaBH4. These highly active Pd NCs are stabilized by surface-coordinated nitroarenes, which inhibit the further growth and aggregation of Pd NCs. By controlling the concentration of Pd(OAc)2 (0.1-0.5 mol% of nitroarene) and NaBH4, the water/ethanol solvent ratio and the tandem reaction sequence, each of the five categories of N-containing compounds can be obtained with excellent yields (up to 98%) in less than 30 min at room temperature. This tunable catalytic tandem reaction works efficiently with a broad range of nitroarene substrates and offers a green and sustainable method for the rapid and large-scale production of valuable N-containing chemicals.
- Yan, Ziqiang,Xie, Xiaoyu,Song, Qun,Ma, Fulei,Sui, Xinyu,Huo, Ziyu,Ma, Mingming
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supporting information
p. 1301 - 1307
(2020/03/11)
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- A general and scalable synthesis of polysubstituted indoles
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A consecutive 2-step synthesis of N-unprotected polysubstituted indoles bearing an electron-withdrawing group at the C-3 position from readily available nitroarenes is reported. The protocol is based on the [3,3]-sigmatropic rearrangement of N-oxyenamines generated by the DABCO-catalyzed reaction of N-arylhydroxylamines and conjugated terminal alkynes, and delivers indoles endowed with a wide array of substitution patterns and topologies.
- Diana-Rivero, Raquel,García-Tellado, Fernando,Tejedor, David
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- Highly Selective and Solvent-Dependent Reduction of Nitrobenzene to N-Phenylhydroxylamine, Azoxybenzene, and Aniline Catalyzed by Phosphino-Modified Polymer Immobilized Ionic Liquid-Stabilized AuNPs
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Gold nanoparticles stabilized by phosphine-decorated polymer immobilized ionic liquids (AuNP@PPh2-PIILP) is an extremely efficient multiproduct selective catalyst for the sodium borohydride-mediated reduction of nitrobenzene giving N-phenylhydroxylamine, azoxybenzene, or aniline as the sole product under mild conditions and a very low catalyst loading. The use of a single nanoparticle-based catalyst for the partial and complete reduction of nitroarenes to afford three different products with exceptionally high selectivities is unprecedented. Under optimum conditions, thermodynamically unfavorable N-phenylhydroxylamine can be obtained as the sole product in near quantitative yield in water, whereas a change in reaction solvent to ethanol results in a dramatic switch in selectivity to afford azoxybenzene. The key to obtaining such a high selectivity for N-phenylhydroxylamine is the use of a nitrogen atmosphere at room temperature as reactions conducted under an inert atmosphere occur via the direct pathway and are essentially irreversible, while reactions in air afford significant amounts of azoxy-based products by virtue of competing condensation due to reversible formation of N-phenylhydroxylamine. Ultimately, aniline can also be obtained quantitatively and selectively by adjusting the reaction temperature and time accordingly. Introduction of PEG onto the polyionic liquid resulted in a dramatic improvement in catalyst efficiency such that N-phenylhydroxylamine could be obtained with a turnover number (TON) of 100000 (turnover frequency (TOF) of 73000 h-1, with >99% selectivity), azoxybenzene with a TON of 55000 (TOF of 37000 h-1 with 100% selectivity), and aniline with a TON of 500000 (TOF of 62500 h-1, with 100% selectivity). As the combination of ionic liquid and phosphine is required to achieve high activity and selectivity, further studies are currently underway to explore whether interfacial electronic effects influence adsorption and thereby selectivity and whether channeling of the substrate by the electrostatic potential around the AuNPs is responsible for the high activity. This is the first report of a AuNP-based system that can selectively reduce nitroarenes to either of two synthetically important intermediates as well as aniline and, in this regard, is an exciting discovery that will form the basis to develop a continuous flow process enabling facile scale-up.
- Doherty, Simon,Knight, Julian G.,Backhouse, Tom,Summers, Ryan J.,Abood, Einas,Simpson, William,Paget, William,Bourne, Richard A.,Chamberlain, Thomas W.,Stones, Rebecca,Lovelock, Kevin R. J.,Seymour, Jake M.,Isaacs, Mark A.,Hardacre, Christopher,Daly, Helen,Rees, Nicholas H.
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p. 4777 - 4791
(2019/05/17)
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- Tandem Chiral Cu(II) Phosphate-Catalyzed Deoxygenation of Nitrones/Enantioselective Povarov Reaction with Enecarbamates
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A new catalytic enantioselective tandem deoxygenation/aza-Diels-Alder reaction of nitrones with enecarbamates was serendipitously discovered in the presence of chiral copper(II) diphosphate complexes. This process affords a wide range of 4-aminotetrahydroquinolines in respectable yields under mild conditions with good to excellent ee values.
- Gelis, Coralie,Levitre, Guillaume,Guérineau, Vincent,Touboul, David,Neuville, Luc,Masson, Géraldine
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supporting information
p. 5151 - 5155
(2019/06/27)
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- Highly Electron-Deficient Pyridinium-Nitrones for Rapid and Tunable Inverse-Electron-Demand Strain-Promoted Alkyne-Nitrone Cycloaddition
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Highly accelerated inverse-electron-demand strain-promoted alkyne-nitrone cycloaddition (IED SPANC) between a stable cyclooctyne (bicyclo[6.1.0]nonyne (BCN)) and nitrones delocalized into a Cα-pyridinium functionality is reported, with the most
- Gunawardene, Praveen N.,Luo, Wilson,Polgar, Alexander M.,Corrigan, John F.,Workentin, Mark S.
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supporting information
p. 5547 - 5551
(2019/08/01)
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- Hydroxamic Acids as Chemoselective (ortho-Amino)arylation Reagents via Sigmatropic Rearrangement
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The use of readily available hydroxamic acids as reagents for the chemoselective (ortho-amino)arylation of amides is described. This reaction proceeds under metal-free, mild conditions, displays a very broad scope, and constitutes a direct approach for the metal-free attachment of aniline residues to carbonyl derivatives.
- Shaaban, Saad,Tona, Veronica,Peng, Bo,Maulide, Nuno
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supporting information
p. 10938 - 10941
(2017/08/30)
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- Synthesis of some new selenonitrone compounds
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The carbonyl selenonitrile and dicarbonyl diselane compounds were prepared by using the inorganic reagent such as potassium selenocyanate. New nitrone compounds were synthesized from the condensation of carbonyl group in the selenocarbonyl compounds with substituted N-phenylhydroxylamine and N-benzyl hydroxylamine. The resulting products were identified by physical properties such as melting point (M.p.), retardation factor (Rf) and color. Also compounds showed the expected data in identification techniques such as FTIR, 1H NMR, 13 C NMR, mass spectroscopy and Elemental analysis (CHN). The results proved the validity of the expected chemical structures of synthesized compounds.
- Haddad, Batool Saleh
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p. 2821 - 2826
(2018/02/20)
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- Influence of the side-group at C=N bridging bond of bis-aryl Schiff bases on the wavelength of absorption maximum of ultraviolet absorption spectra
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The compounds N-(benzylidene)-anilines XArCH=NArY (XBAY), N-(phenyl-ethylene)-anilines XArC(CH3)=NArY (XPEAY) and N-phenyl-α-phenylnitrones XArCH=N(O)ArY (XPNY) have bridging group CH=N, C(CH3)=N and CH=N(O) respectively, in which the C(CH3)=N has a side-group methyl CH3 at carbon end and the CH=N(O) has a side-group O atom at nitrogen end. In this work, a series of XPEAY and XPNY were synthesized, and their longest wavelength maximum λmax (nm) of ultraviolet absorption spectra were measured. Then the change regularity of the νmax (cm-1, νmax=1/λmax) of XPEAY and XPNY were investigated, and they were compared with that of XBAY (reported by ref.26). The results indicate: (1) There are no good linear relationships between the νmax of XBAYs and XPEAYs or XPNYs. (2) In case of a same set of X-Y group couples, the distribution of λmax of XPEAYs is larger than that of XPNYs. (3) The side-group CH3 makes the effect of σ(X) larger than that of σ(Y) on the νmax of XPEAYs, whereas the O atom makes the effect of σ(Y) larger than that of σ(X) on the νmax of XPNYs. (4) The cross-interaction between X and Y has important effect on the all νmax. However, the cross-interaction between CH3 and X/Y has not important effect on the νmax of XPEAY, and the cross-interaction between O and X/Y has not important effect on the νmax of XPNY. Copyright
- Luo, Qingqing,Cao, Chao-Tun,Cao, Zhongzhong,Cao, Chenzhong
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p. 406 - 413
(2016/07/28)
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- Selective conversion of nitroarenes using a carbon nanotube-ruthenium nanohybrid
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Ruthenium nanoparticles were assembled on carbon nanotubes and the resulting nanohybrid was used in the hydrazine-mediated catalytic hydrogenation of various nitroarenes, at room temperature. Depending on the solvent, a selective transformation occurred, giving either access to the corresponding aniline or hydroxylamine derivative.
- Jawale, Dhanaji V.,Gravel, Edmond,Boudet, Caroline,Shah, Nimesh,Geertsen, Valérie,Li, Haiyan,Namboothiri, Irishi N. N.,Doris, Eric
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supporting information
p. 1739 - 1742
(2015/03/03)
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- An asymmetric pericyclic cascade approach to 3-alkyl-3-aryloxindoles: Generality, applications and mechanistic investigations
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The reaction of L-serine derived N-arylnitrones with alkylarylketenes generates asymmetric 3-alkyl-3-aryloxindoles in good to excellent yields (up to 93%) and excellent enantioselectivity (up to 98% ee) via a pericyclic cascade process. The optimization, scope and applications of this transformation are reported, alongside further synthetic and computational investigations. The preparation of the enantiomer of a Roche anti-cancer agent (RO4999200) 1 (96% ee) in three steps demonstrates the potential utility of this methodology.
- Richmond, Edward,Ling, Kenneth B.,Duguet, Nicolas,Manton, Lois B.,elebi-?lcüm, Nihan,Lam, Yu-Hong,Alsancak, Sezen,Slawin, Alexandra M. Z.,Houk,Smith, Andrew D.
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supporting information
p. 1807 - 1817
(2015/02/19)
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- A study on the selective hydrogenation of nitroaromatics to N-arylhydroxylamines using a supported Pt nanoparticle catalyst
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A supported Pt nanoparticle-based catalyst was used in the chemoselective hydrogenation of nitroarenes to N-arylhydroxylamines (N-AHA). Optimization of NB hydrogenation conditions showed that substantially higher N-PHA yields can be obtained at low temperature. Especially, the influence of an increased hydrogen pressure on selectivity is remarkable. Maximum yields increase from 55% N-PHA at 4 bar H2 to 80% at 23 bar H2 in ethanol. Further optimization led to the use of small amounts of amine additive, TMEDA, with 50 bar H2 raising the maximum yield to 97% N-PHA. The decreased N-PHA hydrogenation rate at high H2 pressure and the presence of TMEDA allow for selective transformation of a range of other nitroarenes containing electron-withdrawing and -donating (reducible) functional groups to their N-AHAs in excellent (more than 90%) yields.
- Boymans, Evert H.,Witte,Vogt
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p. 176 - 183
(2015/02/19)
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- Rhodium(III)-catalyzed internal oxidative coupling of N-hydroxyanilides with alkenes via C-H activation
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Abstract Described herein is an efficient new method for ortho-olefination of anilides in the presence of AgSbF6 and NaOAc via rhodium(III)-catalyzed internal oxidative C-H bond activation based on hydroxyl as directing and oxidative group. A range of alkenes and functional groups on acetanilides is supported and a possible mechanism is proposed according to the experimental results.
- Wen, Jing,Wu, An,Chen, Pei,Zhu, Jin
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supporting information
p. 5282 - 5286
(2015/08/26)
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- Modification of fulleropyrazolines modulates their cleavage by light
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The extraordinary electrochemistry and the tunability of their energy levels allows the use of fulleropyrazolines in photovoltaics and charge-transfer systems. Here we show that substitution in position 1 tunes photolytic stability; electron-donating groups facilitate 1,3-dipolar cycloreversion to fullerene. This discovery has implications not only for photovoltaic stability but also highlights a potential strategy for photo-controlled fullerene release systems ('photo-caged'/'photo-activated' fullerene). This journal is
- Rutte, Reida N.,Parsons, Thomas B.,Davis, Benjamin G.
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supporting information
p. 12297 - 12299
(2015/02/19)
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- Synthesis of site-specific damaged DNA strands by 8-(acetylarylamino)- 2′-deoxyguanosine adducts and effects on various DNA polymerases
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Beside the predominately found 8-(arylamino)-2′-dG, 8-(acetylarylamino) damages within DNA-strands may also play an important role in the induction of chemical carcinogenesis. A synthesis pathway leading to these 8-(acetylarylamino)-dG adducts using different aromatic amines has been optimized. The 8-modified dGs were converted into the corresponding phosphoramidites and site-specifically incorporated into different oligonucleotides leading to DNA strands. Lesion-bearing hybrids of these damaged DNA-strands with complementary oligonucleotides were used to study their melting properties and their circular dichroism spectra. It was shown that no EcoRI restriction took place with the damage inside the cleavage site. Finally, three different DNA polymerases were used for primer extension studies. C8-NAc-Arylamine adducts of 2′-deoxyguanosine with various aromatic amines were synthesized by using cross-coupling reactions and converted into 3′-phosphoramidites. Site-specific damaged NarI-, EcoRI- and 20mer-oligonucleotides were prepared by automated DNA-synthesis. Biophysical properties, restriction endonuclease studies and DNA-polymerase assays were performed. Copyright
- Krueger, Sarah,Meier, Chris
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p. 1158 - 1169
(2013/04/10)
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- Interrupted fischer-indole intermediates via oxyarylation of alkenyl boronic acids
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The oxyarylation of alkenyl boronic acids with N-arylbenzhydroxamic acids has been achieved under both copper-mediated and copper-catalyzed conditions to provide access to interrupted Fischer-indole intermediates. This transformation is believed to proceed through a copper-promoted C-O bond forming event followed by a [3,3] rearrangement. The scope of the method is described and mechanistic experiments are discussed.
- Wang, Heng-Yen,Anderson, Laura L.
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supporting information
p. 3362 - 3365
(2013/07/26)
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- Asymmetric pericyclic cascade approach to spirocyclic oxindoles
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The reaction of chiral N-arylnitrones with carbocyclic alkylarylketenes generates spirocyclic oxindoles in good yields and with excellent levels of enantioselectivity (90-99% ee) via a pericyclic cascade process.
- Richmond, Edward,Duguet, Nicolas,Slawin, Alexandra M. Z.,Lebl, Tomas,Smith, Andrew D.
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supporting information; experimental part
p. 2762 - 2765
(2012/07/14)
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- Selective synthesis of N-aryl hydroxylamines by the hydrogenation of nitroaromatics using supported platinum catalysts
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Various substituted nitroaromatics were successfully hydrogenated to the corresponding N-aryl hydroxylamines in excellent yields (up to 99%) using supported platinum catalysts such as Pt/SiO2 under a hydrogen atmosphere (1 bar) at room temperature. The key to the fast and highly selective formation of hydroxylamines is the addition of small amounts of amines such as triethylamine and dimethyl sulfoxide; amines promote the conversion of nitroaromatics, while dimethyl sulfoxide inhibits further hydrogenation of hydroxylamines to anilines. The promotive effect depends on which type of amine and primary amine was most effective. The hydrogenation efficiently proceeded in common organic solvents, including isopropanol, diethyl ether, and acetone. This methodology should extend the application range of conventional solid catalysts to fine chemicals synthesis. The Royal Society of Chemistry 2009.
- Takenaka, Yasumasa,Kiyosu, Takahiro,Choi, Jun-Chul,Sakakura, Toshiyasu,Yasuda, Hiroyuki
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supporting information; experimental part
p. 1385 - 1390
(2010/05/18)
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- Solvent hydrogen bonding and structural influences on the CrVI oxidation of anilines in aqueous acetic acid medium
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The oxidation of meta- and para-substituted anilines by CrVI oxidant, imidazolium fluorochromate (IFC), in aqueous acetic acid mixtures of varying compositions in the presence of p-toluenesulfonic acid (PTS) is first order in IFC and PTS. Michaelis-Menten type kinetics is observed with all of the anilines. The IFC oxidation of 15 meta- and para-substituted anilines at 299-322 K complies with the isokinetic relationship but not to any of the linear free energy relationships. The isokinetic temperature lies within the experimental range. The rate data failed to correlate with macroscopic solvent parameters such as relative permittivity, εr, and ionizing power, Y, correlation of rate data with Kamlet-Taft solvatochromic parameters (hydrogen bond donor acidity, α, hydrogen bond acceptor basicity, β, and dipolarity/polarizability, π*) is linear which suggests that the specific solute-solvent interactions play a dominating role in governing the reactivity.
- Bhuvaneshwari,Elango
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experimental part
p. 242 - 249
(2010/04/26)
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- Design, synthesis, characterization, and preliminary complexation studies of chromogenic vanadophiles: 1,3-alternate thiacalix[4]arene tetrahydroxamic acids
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New chromogenic supramolecular vanadophiles were designed and synthesized by incorporating hydroxamic acid chains on a 1,3-alternate thiacalix[4]arene scaffold and were found to show high affinity toward vanadate ions. The article describes a comprehensive design process to devise a tailor-made co-ordination cavity for vanadate ions by pre-organization of hydroxamic acid chelating moieties on a 1,3-alternate thiacalix[4]arene scaffold. These receptors simultaneously co-ordinate two vanadate ions giving a highly 'staggered' geometry with almost D2d symmetry. Proposed structures and complexation behavior of the receptors were explained by critical examination of FTIR, UV-visible, mass, and 1H NMR data.
- Patel, Mitesh H.,Patel, Vijay B.,Shrivastav, Pranav S.
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p. 2057 - 2062
(2008/09/18)
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- New nitronate σ complexes and the mechanism of nucleophilic aromatic photosubstitution para to a nitro group
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Photolysis of 4-nitroanisole with aliphatic amines gives mainly N-substituted 4-nitroanilines. Reactions of this type have been widely attributed to a geminate radical mechanism. We questioned this interpretation and have searched for and found by NMR spectroscopy a new class of stable nitronate adducts generated under the reaction conditions. The adducts imply that photosubstitution by amines para to the nitro group occurs by meta σ complex formation followed by an unprecedented sigmatropic rearrangement.
- Wubbels, Gene G.,Johnson, Kandra M.
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p. 1451 - 1454
(2007/10/03)
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- Effect of solvent on the rate of oxidation of substituted anilines with nicotinium dichromate in aqueous-acetic acid media
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Mechanistic studies on the oxidation of 15 para- and meta-substituted anilines by nicotinium dichromate in water-acetic acid medium of varying mole fractions have been performed. The reaction can be characterized by the experimental rate equation, -d[oxidizing agent]/dt = Kk [substrate] [HCrO 4-]/(1 + K [substrate]) The addition of p-toluenesulfonic acid enhances the reaction. The oxidation substituted anilines at 299-322 K complies with the isokinetic relationship but not to any of the linear free energy relationships, the isokinetic temperature lies within the experimental range. Correlation of rate data with Kamlet-Taft solvatochromic parameters (α, β, π*) suggests that the specific solute-solvent interactions play a major role in governing the reactivity.
- Bhuvaneshwari,Elango
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p. 999 - 1005
(2007/10/03)
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- Effect of substituents on the rate of oxidation of anilines with peroxomonosulfate monoanion (HOOSO3-) in aqueous acetonitrile: A mechanistic study
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Mechanistic studies on the oxidation of 18 meta-, para-, and ortho-substituted anilines (Ans) by HOOSO3- in aqueous acetonitrile medium have been performed. The reaction can be characterized by the experimental rate equation, -d[HSO5-]/dt = k[An][HSO5-] The addition of p-toluenesulfonic acid (TsOH) retards the reaction. The increase in the reactivity of anilines as the medium is made more aqueous is interpreted. The reaction is enhanced by electron-donating groups on the amine in the series consistent with the rate-limiting nucleophilic attack of the amine on the persulfate oxygen. The proposed mechanism involves the conversion of phenylhydroxylamine to nitrosobenzene in a fast step. The ESR study reveals the absence of free radicals in the reaction. Various attempts have been made to analyze the experimental rate constants in terms of LFER plots. Improved correlations are obtained with σ- values and the σ- form of the Yukawa-Tsuno equation.
- Meenakshisundaram, Subbiah,Selvaraju,Made Gowda,Rangappa, Kanchugarakoppal S.
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p. 649 - 657
(2007/10/03)
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- Mechanism and reactivity in perborate oxidation of anilines in acetic acid
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Perborate but not percarbonate in acetic acid generates peracetic acid on standing and the peracetic acid oxidation of anilines is fast. The oxidation with a fresh solution of perborate in acetic acid is smooth and second order but the specific oxidation rate increases with increasing [perborate]0 or [boric acid]. Perborate on dissolution affords hydrogen peroxide and a borate; the latter assists the former in the oxidation. The oxidation rates of anilines under identical conditions do not conform to any of the linear free energy relationships but the reaction rates of molecular anilines do. Perborate oxidation proceeds via two reaction paths but the overall oxidation rates of molecular anilines conform to structure reactivity relationships; the transition states do not differ significantly. Analysis of the oxidation rates of perborate and percarbonate reveals that while perborate oxidation is faster than percarbonate it is at least as selective as the latter.
- Karunakaran, Chockalingam,Kamalam, Ramasamy
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p. 2011 - 2018
(2007/10/03)
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- para-Substituted N-Nitroso-N-oxybenzenamine ammonium salts: A new class of redox-sensitive nitric oxide releasing compounds
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N-Nitroso-N-oxybenzenamine ammonium salts with -OMe, -Me, -H, -F, -Cl, - CF3, and -SO2Me substituents at the para position of the phenyl ring constitute a new class of-redox sensitive nitric oxide (NO) releasing compounds. These compounds yield nitric oxide and the corresponding nitrosobenzene derivatives by a spontaneous dissociation mechanism after undergoing a one electron oxidation. Oxidation of these compounds can be achieved through chemical, electrochemical and enzymatic methods. It was observed electrochemically that the amount of NO generated was dependent on the substituent effect and the applied oxidation potential. Electron- withdrawing substituents increase the oxidation potential of the compound. A linear correlation was observed when the peak potentials for the oxidation were graphed versus the Hammett substituent constant. Density functional theory calculations were also performed on this series of compounds. The theoretical oxidation energies of the corresponding anions show a strong linear correlation with the experimental potentials. Furthermore, enzymatic oxidation using horseradish peroxidase showed a similar substituent effect. These results indicate that substitution at the para position of the phenyl ring has a profound effect on the stability, oxidation potential and enzymatic kinetic properties of the compounds. Thus para-substituted N- nitroso-N-oxybenzenamine salts comprise a new class of redox-sensitive nitric oxide releasing agents. (C) 2000 Elsevier Science Ltd.
- McGill, Andrea D.,Zhang, Wei,Wittbrodt, Joanne,Wang, Jianqiang,Schlegel, H. Bernhard,Wang, Peng George
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p. 405 - 412
(2007/10/03)
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- The powerful effect of N-aryl substitution in promoting the thermal rearrangement of 5-spirocyclopropaneisoxazolidines
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N-Alkyl 5-spirocyclopropaneisoxazolidines rearrange to tetrahydropyridone derivatives by heating. The presence of a phenyl ring on the nitrogen atom significantly reduces the rearrangement temperature. This effect is enhanced by electron-donating substituents and reduced by electron- withdrawing substituents on the phenyl ring.
- Cordero, Franca M.,Barile, Ingrid,De Sarlo, Francesco,Brandi, Alberto
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p. 6657 - 6660
(2007/10/03)
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- Kinetics and Mechanism of Oxidation of para-Substituted Anilines by Peroxomonosulphate
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Kinetics of oxidation of several para-substituted anilines by peroxomonosulphate (PMS) in aqueous acetic acid medium have been investigated. The reaction follows a total second order, first order each in [PMS] and [substrate]. The reaction rate is retarted by both electron-releasing and withdrawing groups. Absence of free radical formation is confirmed. Activation energy and thermodynamic parameters have been computed. A probable mechanism has been proposed.
- Abdul Jameel,Maruthamuthu
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p. 368 - 370
(2007/10/03)
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- Synthesis of N-arylhydroxylamines by antimony-catalyzed reduction of nitroarenes
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Metallic antimony catalyzes the reduction of aromatic nitro compounds to the corresponding N-arylhydroxylamines in good yields with NaBH4 under mild conditions. The azoxybenzenes from autoxidation of N-arylhydroxylamines were also obtained in basic conditions.
- Ren, Pingda,Dong, Tingwei,Wu, Shihui
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p. 1547 - 1552
(2007/10/03)
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- A facile synthesis of N-aryl-N-hydroxyformamides from N-arylhydroxylamines
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Several N-arylhydroxylamines (2) have been formylated for the first time with acetic formic anhydride to yield N-hydroxyformanilides (3) in better yields than hitherto reported.
- Ayyangar, N. R.,Brahme, K. C.,Shingare, M. S.,Srinivasan, K. V.
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p. 961 - 963
(2007/10/02)
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- Acid-Catalyzed Hydrolysis of N-Hydroxyacetanilides: Amide Hydrolysis vs N-O Bond Heterolysis
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Although it has been widely assumed that N-hydroxy-N-aryl amides decompose in acidic solution by acid-catalyzed N-O bond heterolysis, we have found that the N-hydroxyacetanilides 1a-e largely decompose by the alternative amide hydrolysis pathway.The immediate products of hydrolysis, the hydroxylamines 2a-e, can be detected by direct or indirect methods, but these materials also decompose via the Bamberger rearrangement under the reaction conditions.Only the p-EtO- and p-MeO-substituted N-hydroxyacetanilides (1a and 1b) exhibit any sign of N-O bond heterolysis, and only as a minor component (ca. 7percent) of the overall hydrolysis.No change in mechanism could be found for 1d in H2SO4 solutions as concentrated as 9 M.The lack of reactivity of 1a-e to N-O bond heterolysis is largely due to unfavorable protonation of the OH group.Protonation of the carbonyl oxygen is favored over the hydroxyl oxygen by ca. 7 orders of magnitude.
- Novak, Michael,Bonham, Gayl A.,Mohler, Linda K.,Peet, Kristine M.
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p. 3903 - 3908
(2007/10/02)
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- Hetero-Cope Rearrangements, III. - Vinylindoles via Hetero-Cope Rearrangement
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The reaction of N-phenylnitrones 1 with allenes 2 which are substituted with electron acceptor groups gives various products via addition and sigmatropic rearrangement depending on the specific acceptor group.In this manner one obtains 2-substituted indoles 8a, 8b, and 10 from propadienyl trichloromethyl sulfoxide.Using phenyl propadienyl sulfone a derivative 4a of tetrahydro-1-benzazepin-4-one is obtained.Reactions with allenecarbonitril proceed via several steps and yield 2-vinylindoles of type 6.Intermediate products could not be isolated.
- Blechert, Siegfried
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p. 673 - 682
(2007/10/02)
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