- pH Dependence of the Lifetime of a Norrish II Biradical
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The transient spectroscopy of γ-phenylbutyrophenone in a 2:1 (v/v) methanol:water mixture has been studied as a function of pH.The lifetime of the Norrish II 1,4-biradical shows an excellent titration curve.The moderately strongly absorbing acidic form of the biradical has a lifetime of 125 ns, with λmax of the difference spectrum with starting material at 320 nm.The strongly absorbing basic form has a lifetime of 62 ns and λmax 325 nm.The pKa in the mixed solvent is 11.8.The pKa in pure water, based on solvent dependence of pKa values for phenols of similar acidity, is estimated as 10.2+/-0.2, essentially identical with a value reported for the acetophenone ketyl monoradical.
- Caldwell, Richard A.,Dhawan, S. N.,Moore, D. E.
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Read Online
- Subphthalocyanine encapsulated within MIL-101(Cr)-NH2 as a solar light photoredox catalyst for dehalogenation of α-haloacetophenones
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Subphthalocyanine has been incorporated into a robust metal-organic framework having amino groups as binding sites. The resulting SubPc?MIL-101(Cr)-NH2 composite has a loading of 2 wt%. Adsorption of subphthalocyanine does not deteriorate host crystallinity, but decreases the surface area and porosity of MIL-101(Cr)-NH2. The resulting SubPc?MIL-101(Cr)-NH2 composite exhibits a 575 nm absorption band responsible for the observed photoredox catalytic activity under simulated sunlight irradiation for hydrogenative dehalogenation of α-haloacetophenones and for the coupling of α-bromoacetophenone and styrene. The material undergoes a slight deactivation upon reuse. In comparison to the case of phthalocyanines the present study is one of the few cases showing the use of subphthalocyanine as a photoredox catalyst, with its activity derived from site isolation within the MOF cavities.
- Santiago-Portillo, Andrea,Remiro-Buenama?ana, Sonia,Navalón, Sergio,García, Hermenegildo
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Read Online
- Photocatalyzed Decarboxylative Thiolation of Carboxylic Acids Enabled by Fluorinated Disulfide
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Thiolation of carboxylic acids using a disulfide reagent having tetrafluoropyridinyl groups is described. The light-mediated process is performed using an acridine-type photocatalyst. Primary, secondary, tertiary, and heteroatom-substituted carboxylic acids can be thiolated, and the method can be applied to the late-stage modification of a range of naturally occurring compounds and drugs. The fluorinated pyridine fragment is believed to enable the C-S bond formation. The resulting sulfides were used as redox-active radical precursors.
- Zubkov, Mikhail O.,Kosobokov, Mikhail D.,Levin, Vitalij V.,Dilman, Alexander D.
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supporting information
p. 2354 - 2358
(2022/04/07)
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- Nickel-Catalyzed Reductive Acylation of Carboxylic Acids with Alkyl Halides and N-Hydroxyphthalimide Esters Enabled by Electrochemical Process
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A sustainable Ni-catalyzed reductive acylation reaction of carboxylic acids via an electrochemical pathway is presented, affording a variety of ketones as major products. The reaction proceeds at ambient temperature using unactivated alkyl halides and N-hydroxyphthalimide (NHP) esters as coupling partners, which exhibits several synthetic advantages, including mild conditions and convenience of amplification (58% yield for 6 mmol scale reaction). (Figure presented.).
- Guo, Lin,Xia, Raymond Yang,Xia, Wujiong,Yang, Chao,Zhang, Haoxiang,Zhou, Xiao
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supporting information
(2022/03/31)
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- Rh-Catalyzed Coupling of Aldehydes with Allylboronates Enables Facile Access to Ketones
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We present herein a novel strategy for the preparation of ketones from aldehydes and allylic boronic esters. This reaction involves the allylation of aldehydes with allylic boronic esters and the Rh-catalyzed chain-walking of homoallylic alcohols. The key to this successful development is the protodeboronation of alkenyl borylether intermediate via a tetravalent borate anion species in the presence of KHF2 and MeOH. This approach features mild reaction conditions, broad substrate scope, and excellent functional group tolerance. Mechanistic studies also supported that the tandem allylation and chain-walking process were involved.
- Zhang, Kezhuo,Huang, Jiaxin,Zhao, Wanxiang
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supporting information
(2022/02/21)
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- Direct Addition of Grignard Reagents to Aliphatic Carboxylic Acids Enabled by Bulky turbo-Organomagnesium Anilides
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The synthesis of ketones through addition of organometallic reagents to aliphatic carboxylic acids is a straightforward strategy that is limited to organolithium reagents. More desirable Grignard reagents can be activated and controlled with a bulky aniline-derived turbo-Hauser base. This operationally simple procedure allows the straightforward preparation of a variety of aliphatic and perfluoroalkyl ketones alike from functionalized alkyl, aryl and heteroaryl Grignard reagents.
- Colas, Kilian,Kohlhepp, Stefanie V.,Mendoza, Abraham,V. D. dos Santos, A. Catarina
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supporting information
(2022/02/02)
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- A Proton-Responsive Pyridyl(benzamide)-Functionalized NHC Ligand on Ir Complex for Alkylation of Ketones and Secondary Alcohols
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A Cp*Ir(III) complex (1) of a newly designed ligand L1 featuring a proton-responsive pyridyl(benzamide) appended on N-heterocyclic carbene (NHC) has been synthesized. The molecular structure of 1 reveals a dearomatized form of the ligand. The protonation of 1 with HBF4 in tetrahydrofuran gives the corresponding aromatized complex [Cp*Ir(L1H)Cl]BF4 (2). Both compounds are characterized spectroscopically and by X-ray crystallography. The protonation of 1 with acid is examined by 1H NMR and UV-vis spectra. The proton-responsive character of 1 is exploited for catalyzing α-alkylation of ketones and β-alkylation of secondary alcohols using primary alcohols as alkylating agents through hydrogen-borrowing methodology. Compound 1 is an effective catalyst for these reactions and exhibits a superior activity in comparison to a structurally similar iridium complex [Cp*Ir(L2)Cl]PF6 (3) lacking a proton-responsive pendant amide moiety. The catalytic alkylation is characterized by a wide substrate scope, low catalyst and base loadings, and a short reaction time. The catalytic efficacy of 1 is also demonstrated for the syntheses of quinoline and lactone derivatives via acceptorless dehydrogenation, and selective alkylation of two steroids, pregnenolone and testosterone. Detailed mechanistic investigations and DFT calculations substantiate the role of the proton-responsive ligand in the hydrogen-borrowing process.
- Kaur, Mandeep,U Din Reshi, Noor,Patra, Kamaless,Bhattacherya, Arindom,Kunnikuruvan, Sooraj,Bera, Jitendra K.
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supporting information
p. 10737 - 10748
(2021/06/15)
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- Nickel-catalyzed α-alkylation of ketones with benzyl alcohols
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We reported an efficient method for α-alkylation of ketones with benzyl alcohols using the pyridine-bridged pincer-type N-heterocyclic carbenes nickel complexes as catalysts. A wide range of ketones and benzyl alcohols were efficiently converted into various alkylated products in moderate to high yields. In addition, these nickel complexes were also successfully applied for the synthesis of a wide range of quinoline derivatives.
- Li, Min,Liu, Jichang,Liu, Ning,Shi, Lei,Wang, Yubin,Wu, Di
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- Hantzsch Ester-Mediated Photochemical Transformations in the Ketone Series: Remote C(sp3)-H Arylation and Cyclopentene Synthesis through Strain Release
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A metal-free Hantzsch ester-mediated synthesis of cyclopentenylketones as well as O-hetarylketones starting from ketocyclopropanes under eco-friendly conditions was developed. The versatility of the developed conditions is shown by reacting ketocyclopropanes in both a formal [3 + 2] cycloaddition with terminal alkynes (further investigated using theoretical calculations) and a radical C-C-coupling with cyanopyridines. The newly developed methodologies were later on utilized as a downstream reaction for photogenerated cyclopropanes combining UV and visible light photochemistry. Following this procedure, a UV-driven Norrish-Yang-type reaction induces the ring strain of the intermediates, which serves as activation energy for the subsequent ring transformation.
- Paternoga, Jan,Kühlborn, Jonas,Rossdam, Nils Ole,Opatz, Till
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p. 3232 - 3248
(2021/02/27)
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- Vinyl Azides as Radical Acceptors in the Vitamin B12-Catalyzed Synthesis of Unsymmetrical Ketones
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Vinyl azides are very reactive species and as such are useful building blocks, in particular, in the synthesis of N-heterocycles. They can also serve as precursors of ketones. These form in reactions of vinyl azides with nucleophiles or radicals. We have found, however, that under light irradiation vitamin B12 catalyzes the reaction of vinyl azides with electrophiles to afford unsymmetrical carbonyl compounds in decent yields. Mechanistic studies revealed that alkyl radicals are key intermediates in this transformation.
- Dworakowski, Krzysztof R.,Pisarek, Sabina,Hassan, Sidra,Gryko, Dorota
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supporting information
p. 9068 - 9072
(2021/11/30)
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- Visible-light induced metal-free cascade Wittig/hydroalkylation reactions
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Cascade reactions are green and powerful transformations for building multiple carbon-carbon bonds in one step. Through a relay olefination and radical addition process, we were able to develop the cascade Wittig/hydroalkylation reactions induced by visible light. This metal-free radical approach features mild conditions, robustness, and excellent functionality compatibility. It allows access to saturated C3 homologation products directly from aldehydes or ketones. The synthetic utility of this method is demonstrated by a two-step synthesis ofindolizidine 209D.
- Miao, Pannan,Li, Ruining,Lin, Xianfeng,Rao, Liangming,Sun, Zhankui
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p. 1638 - 1641
(2021/03/09)
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- Ground-State Electron Transfer as an Initiation Mechanism for Biocatalytic C-C Bond Forming Reactions
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The development of non-natural reaction mechanisms is an attractive strategy for expanding the synthetic capabilities of substrate promiscuous enzymes. Here, we report an "ene"-reductase catalyzed asymmetric hydroalkylation of olefins using α-bromoketones as radical precursors. Radical initiation occurs via ground-state electron transfer from the flavin cofactor located within the enzyme active site, an underrepresented mechanism in flavin biocatalysis. Four rounds of site saturation mutagenesis were used to access a variant of the "ene"-reductase nicotinamide-dependent cyclohexanone reductase (NCR) from Zymomonas mobiles capable of catalyzing a cyclization to furnish β-chiral cyclopentanones with high levels of enantioselectivity. Additionally, wild-type NCR can catalyze intermolecular couplings with precise stereochemical control over the radical termination step. This report highlights the utility for ground-state electron transfers to enable non-natural biocatalytic C-C bond forming reactions.
- Fu, Haigen,Lam, Heather,Emmanuel, Megan A.,Kim, Ji Hye,Sandoval, Braddock A.,Hyster, Todd K.
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supporting information
p. 9622 - 9629
(2021/07/01)
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- Selective electrochemical oxidation of aromatic hydrocarbons and preparation of mono/multi-carbonyl compounds
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A selective electrochemical oxidation was developed under mild condition. Various mono-carbonyl and multi-carbonyl compounds can be prepared from different aromatic hydrocarbons with moderate to excellent yield and selectivity by virtue of this electrochemical oxidation. The produced carbonyl compounds can be further transformed into α-ketoamides, homoallylic alcohols and oximes in a one-pot reaction. In particular, a series of α-ketoamides were prepared in a one-pot continuous electrolysis. Mechanistic studies showed that 2,2,2-trifluoroethan-1-ol (TFE) can interact with catalyst species and generate the corresponding hydrogen-bonding complex to enhance the electrochemical oxidation performance. [Figure not available: see fulltext.]
- Li, Zhibin,Zhang, Yan,Li, Kuiliang,Zhou, Zhenghong,Zha, Zhenggen,Wang, Zhiyong
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p. 2134 - 2141
(2021/09/29)
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- Iron-Catalyzed, Iminyl Radical-Triggered Cascade 1,5-Hydrogen Atom Transfer/(5+2) or (5+1) Annulation: Oxime as a Five-Atom Assembling Unit
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By integration of iminyl radical-triggered 1,5-hydrogen atom transfer and (5+2) or (5+1) annulation processes, a series of structurally novel and interesting azepine and spiro-tetrahydropyridine derivatives have been successfully prepared in moderate to good yields. This method utilizes FeCl2 as the catalyst and readily available oximes as five-atom units, while showcasing broad substrate scope and good functional group compatibility. The annulation products can be easily converted into many valuable compounds. Moreover, DFT calculation studies are performed to provide some insights into the possible reaction mechanisms for the (5+2) and (5+1) annulations.
- Chen, Ying-Chun,Du, Fei,Jiang, Kun,Liang, Wu,Ouyang, Qin,Shuai, Li,Wei, Ye,Yang, Jie
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p. 19222 - 19228
(2020/08/25)
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- Versatile formation of Ru(II) hydrazone complexes: Structure, theoretical studies and catalytic activity in α-alkylation
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New 1-(anthracen-10-yl)methylene)-2-(benzo[d]thiazol-2-yl)hydrazine (BHA) and 1-(anthracen-10-yl)methylene)-2-(quinolin-2-yl)hydrazine (QHA) ligands were reacted with [RuHCl(CO)(E)3] (E = PPh3 or AsPh3) or [RuCl2(AsPh3)3] in a 1:1 mol ratio in chloroform-ethanol medium to synthesis new ruthenium complexes. All the new ruthenium complexes were analyzed by elemental analysis, IR, NMR (1H, 13C and 31P) spectroscopy, ESI-Mass spectrometry and single crystal XRD techniques. The single crystal XRD study reveals the octahedral geometry around the ruthenium ion. The study also shows that the ligands coordinate with the Ru metal as monoanionic bidentate N^N donors in complexes 1, 3 and 4 and as a neutral bidentate N^N donor in complex 2 by forming five or four member chelate rings. The intramolecular interactions in the crystal lattices were studied by Hirshfeld surface analysis. The results indicate that π-stacking contacts play an important role in the crystal lattices. DFT calculations were carried out to explain the solid structures of complexes 1–3. Moreover, the synthesized complexes were screened as catalysts for the α-alkylation of ketones with alcohols. The effect of various parameters, such as base, solvent, temperature, time, substituents and also catalyst loading, on the catalytic activity were analyzed. The results depict that the complex 3 was found to be an efficient catalyst for the synthesis of α-alkylation products.
- Kavitha, Venkatachalam,Murugan, Kaliyappan,Vijayapritha, Subbarayan,Viswanathamurthi, Periasamy
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- Manganese-Catalyzed Hydroarylation of Unactivated Alkenes
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Transition-metal-catalyzed hydroarylation of unactivated alkenes with strategic use of remote coordinating functional groups has received significant attention recently to address the issues of both low reactivity and poor selectivity. The bidentate 8-aminoquinoline amide group is the most successfully adopted in unactivated alkenes for Pd and Ni catalysis. We describe the first manganese-catalyzed hydroarylation of unactivated alkenes bearing diverse simple functionalities with arylboronic acids. A series of δ- and γ-arylated amides, ketones, pyridines, and amines was accessed with excellent regioselectivity and in high yields. Hydroalkenylation of unactivated alkenes was also shown to be applicable under this manganese-catalysis regime. The method features earth-abundant manganese catalysis, easily available substrates, broad functional-group tolerance, and excellent regioselective control.
- Liu, Ting,Wang, Congyang,Yang, Yunhui
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supporting information
p. 14256 - 14260
(2020/07/13)
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- Regioselective Vinylation of Remote Unactivated C(sp3)?H Bonds: Access to Complex Fluoroalkylated Alkenes
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Regioselective incorporation of a particular functional group into aliphatic sites by direct activation of unreactive C?H bonds is of great synthetic value. Despite advances in radical-mediated functionalization of C(sp3)?H bonds by a hydrogen-atom transfer process, the site-selective vinylation of remote C(sp3)?H bonds still remains underexplored. Reported herein is a new protocol for the regioselective vinylation of unactivated C(sp3)?H bonds. The remote C(sp3)?H activation is promoted by a C-centered radical instead of the commonly used N and O radicals. The reaction possesses high product diversity and synthetic efficiency, furnishing a plethora of synthetically valuable E alkenes bearing tri-/di-/mono-fluoromethyl and perfluoroalkyl groups.
- Wu, Shuo,Wu, Xinxin,Wang, Dongping,Zhu, Chen
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p. 1499 - 1503
(2019/01/04)
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- Photoredox Reaction of 2-Mercaptothiazolinium Salts with Silyl Enol Ethers
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A method for the generation of free radicals from thiazolinium salts upon photocatalytic reduction is described. The thiazolinium salts are generated by treatment with methyl triflate of 2-mercaptothiazolines, which can be readily obtained from alkyl bromides and tosylates via a nucleophilic substitution reaction or by hydrothiolation of alkenes. Silyl enol ethers were used to trap the radicals, furnishing ketones after successive single-electron oxidation and elimination of the silyl cation.
- Zemtsov, Artem A.,Ashirbaev, Salavat S.,Levin, Vitalij V.,Kokorekin, Vladimir A.,Korlyukov, Alexander A.,Dilman, Alexander D.
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- Mn-Enabled Radical-Based Alkyl-Alkyl Cross-Coupling Reaction from 4-Alkyl-1,4-dihydropyridines
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Highly efficient alkylation of β-chloro ketones and their derivatives was achieved by means of domino dehydrochlorination/Mn-enabled radical-based alkyl-alkyl cross-coupling reaction. In situ-generated α,β-unsaturated ketones and their analogues were identified as the reaction intermediates. Known bioactive compounds, such as melperone and azaperone, could be easily prepared from β-chloropropiophenone in two steps.
- Wang, Jie,Pang, Yu-Bo,Tao, Na,Zeng, Run-Sheng,Zhao, Yingsheng
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p. 15315 - 15322
(2019/11/19)
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- Ketones from Nickel-Catalyzed Decarboxylative, Non-Symmetric Cross-Electrophile Coupling of Carboxylic Acid Esters
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Synthesis of the C?C bonds of ketones relies upon one high-availability reagent (carboxylic acids) and one low-availability reagent (organometallic reagents or alkyl iodides). We demonstrate here a ketone synthesis that couples two different carboxylic acid esters, N-hydroxyphthalimide esters and S-2-pyridyl thioesters, to form aryl alkyl and dialkyl ketones in high yields. The keys to this approach are the use of a nickel catalyst with an electron-poor bipyridine or terpyridine ligand, a THF/DMA mixed solvent system, and ZnCl2 to enhance the reactivity of the NHP ester. The resulting reaction can be used to form ketones that have previously been difficult to access, such as hindered tertiary/tertiary ketones with strained rings and ketones with α-heteroatoms. The conditions can be employed in the coupling of complex fragments, including a 20-mer peptide fragment analog of Exendin(9–39) on solid support.
- Wang, Jiang,Cary, Brian P.,Beyer, Peyton D.,Gellman, Samuel H.,Weix, Daniel J.
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p. 12081 - 12085
(2019/08/12)
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- Balancing Bulkiness in Gold(I) Phosphino-triazole Catalysis
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The syntheses of a series of 1-phenyl-5-phosphino 1,2,3-triazoles are disclosed, within which, the phosphorus atom (at the 5-position of a triazole) is appended by one, two or three triazole motifs, and the valency of the phosphorus(III) atom is completed by two, one or zero ancillary (phenyl or cyclohexyl) groups respectively. This series of phosphines was compared with tricyclohexylphosphine and triphenylphosphine to study the effect of increasing the number of triazoles appended to the central phosphorus atom from zero to three triazoles. Gold(I) chloride complexes of the synthesised ligands were prepared and analysed by techniques including single-crystal X-ray diffraction structure determination. Gold(I) complexes were also prepared from 1-(2,6-dimethoxy)-phenyl-5-dicyclohexyl-phosphino 1,2,3-triazole and 1-(2,6-dimethoxy)-phenyl-5-diphenyl-phosphino 1,2,3-triazole ligands. The crystal structures thus obtained were examined using the SambVca (2.0) web tool and percentage buried volumes determined. The effectiveness of these gold(I) chloride complexes to serve as precatalysts for alkyne hydration were assessed. Furthermore, the regioselectivity of hydration of but-1-yne-1,4-diyldibenzene was probed.
- Zhao, Yiming,Wakeling, Matthew G.,Meloni, Fernanda,Sum, Tze Jing,van Nguyen, Huy,Buckley, Benjamin R.,Davies, Paul W.,Fossey, John S.
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p. 5540 - 5548
(2019/08/07)
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- Rhodium Porphyrin Catalyzed Regioselective Transfer Hydrogenolysis of C-C σ-Bonds in Cyclopropanes with iPrOH
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A new rhodium porphyrin catalyzed regioselective transfer hydrogenolysis of both activated and unactivated cyclopropanes employing iPrOH as the hydrogen source was discovered. The reaction mechanism for the C-C σ-bond activation of cyclopropanes was identified through an initial radical substitution with rhodium(II) metalloporphyrin radical to give a rhodium porphyrin alkyl, followed by hydrogenolysis with iPrOH to give the corresponding acyclic alkanes and regenerate rhodium(II) metalloporphyrin radical.
- Chen, Chen,Feng, Shiyu,Chan, Kin Shing
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p. 2582 - 2589
(2019/07/02)
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- Photoenzymatic Catalysis Enables Radical-Mediated Ketone Reduction in Ene-Reductases
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Flavin-dependent ene-reductases (EREDs) are known to stereoselectively reduce activated alkenes, but are inactive toward carbonyls. Demonstrated here is that in the presence of photoredox catalysts, these enzymes will reduce aromatic ketones. Mechanistic experiments suggest this reaction proceeds through ketyl radical formation, a reaction pathway that is distinct from the native hydride-transfer mechanism. Furthermore, this reactivity is accessible without modification of either the enzyme or cofactors, allowing both native and non-natural mechanisms to occur simultaneously. Based on control experiments, we hypothesize that binding to the enzyme active site attenuates the reduction potential of the substrate, enabling single-electron reduction. This reactivity highlights opportunities to access new catalytic manifolds by merging photoredox catalysis with biocatalysis.
- Sandoval, Braddock A.,Kurtoic, Sarah I.,Chung, Megan M.,Biegasiewicz, Kyle F.,Hyster, Todd K.
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supporting information
p. 8714 - 8718
(2019/05/28)
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- Reductive C-C Coupling by Desulfurizing Gold-Catalyzed Photoreactions
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[Au2(μ-dppm)2]Cl2-mediated photocatalysis reactions are usually initiated by ultraviolet A (UVA) light; herein, an unreported system using blue light-emitting diodes (LEDs) as excitation light source was found. The red shift of the absorption wavelength originates from the combination of [Au2(μ-dppm)2]Cl2 and ligand (Ph3P or mercaptan). On the basis of this finding, a gold-catalyzed reductive desulfurizing C-C coupling of electrophilic radicals and styrenes mediated by blue LEDs is presented, a coupling which cannot be efficiently accessed by previously reported methods. This mild and highly efficient C-C bond formation strategy uses mercaptans both as electron-deficient alkyl radical precursor as well as the hydrogen source. Two examples of amino acids have also been modified by using this strategy. Moreover, this methodology could be applied in polymer synthesis. Gram-scale synthesis and mechanistic insights into this transformation are also presented.
- Zhang, Lumin,Si, Xiaojia,Yang, Yangyang,Witzel, Sina,Sekine, Kohei,Rudolph, Matthias,Rominger, Frank,Hashmi, A. Stephen K.
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p. 6118 - 6123
(2019/07/03)
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- Iron-Catalysed Remote C(sp3)?H Azidation of O-Acyl Oximes and N-Acyloxy Imidates Enabled by 1,5-Hydrogen Atom Transfer of Iminyl and Imidate Radicals: Synthesis of γ-Azido Ketones and β-Azido Alcohols
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In the presence of a catalytic amount of iron(III) acetylacetonate [Fe(acac)3], the reaction of structurally diverse ketoxime esters with trimethylsilyl azide (TMSN3) afforded γ-azido ketones in good to excellent yields. This unprecedented distal γ-C(sp3)?H bond azidation reaction went through a sequence of reductive generation of an iminyl radical, 1,5-hydrogen atom transfer (1,5-HAT) and iron-mediated redox azido transfer to the translocated carbon radical. TMSN3 served not only as a nitrogen source to functionalise the unactivated C(sp3)?H bond, but also as a reductant to generate the catalytically active FeII species in situ. Based on the same principle, a novel β-C(sp3)?H functionalisation of alcohols via N-acyloxy imidates was subsequently realised, leading, after hydrolysis of the resulting ester, to β-azido alcohols, which are important building blocks in organic and medicinal chemistry.
- Torres-Ochoa, Rubén O.,Leclair, Alexandre,Wang, Qian,Zhu, Jieping
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supporting information
p. 9477 - 9484
(2019/05/21)
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- Mild Cu-Catalyzed Oxidation of Benzylic Boronic Esters to Ketones
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The oxidation of benzylic boronic esters directly to the ketone is reported. This mild Cu-catalyzed method uses an ambient atmosphere of air as the terminal oxidant and is notably chemoselective. Oxidation of the C-B bond occurs selectively, even in the presence of unprotected alcohols. Initial investigation suggests the reaction proceeds through an alkylboron to Cu transmetalation, peroxide formation, and rearrangement to give the carbonyl.
- Grayson, James D.,Partridge, Benjamin M.
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p. 4296 - 4301
(2019/05/14)
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- Metal-free visible light photoredox enables generation of carbyne equivalents via phosphonium ylide C-H activation
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Carbyne, an interesting synthetic intermediate, has recently been generated from hypervalent iodine precursors via photoredox catalysis. Given the underexplored chemistry of carbyne, due to the paucity of carbyne sources, we are intrigued to discover a new source for this reactive species from classical reagents-phosphonium ylides. Our novel strategy employing phosphonium ylides in an olefin hydrocarbonation reaction features a facile approach for constructing carbon-carbon bonds through metal-free and benign reaction conditions. Moreover, the hydrocarbonation products were delivered in a highly regioselective manner.
- Das, Mrinmoy,Vu, Minh Duy,Zhang, Qi,Liu, Xue-Wei
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p. 1687 - 1691
(2019/02/14)
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- Manganese-Catalyzed α-Alkylation of Ketones, Esters, and Amides Using Alcohols
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Herein we report the manganese-catalyzed C-C bond-forming reactions via α-alkylation of ketones, amides, and esters, using primary alcohols. β-Alkylation of secondary alcohols by primary alcohols to obtain α-alkylated ketones is also reported. The reactions are catalyzed by a (iPr-PNP)Mn(H)(CO)2 pincer complex under mild conditions in the presence of (catalytic) base liberating water (and H2 in the case of secondary alcohol alkylation) as the sole byproduct.
- Chakraborty, Subrata,Daw, Prosenjit,Ben David, Yehoshoa,Milstein, David
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p. 10300 - 10305
(2018/10/20)
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- Palladium/NHC (NHC = N-Heterocyclic Carbene)-Catalyzed B-Alkyl Suzuki Cross-Coupling of Amides by Selective N-C Bond Cleavage
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A highly chemoselective, palladium-NHC (NHC = N-heterocyclic carbene)-catalyzed, direct cross-coupling between B-sp3-alkyl reagents and activated amides by N-C(O) cleavage is reported. Palladium-NHC precatalysts promote chemoselective alkylations of amides that are inaccessible by applying strong organometallic reagents. Various amides, including challenging primary amides after direct and site-selective N,N-di-Boc activation, are compatible with this method. The potential of this mild protocol is demonstrated in sequential C(sp2)-C(sp2)/C(sp2)-C(sp3) cross-couplings deploying a di-Boc amide derived from a common primary amide bond. The method provides a rare example of air- and moisture-stable, well-defined, and highly reactive Pd-NHC precatalysts in B-alkyl-Suzuki cross-couplings.
- Meng, Guangrong,Szostak, Michal
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supporting information
p. 6789 - 6793
(2018/11/21)
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- Switchable Decarboxylative Heck-Type Reaction and Oxo-alkylation of Styrenes with N-Hydroxyphthalimide Esters under Photocatalysis
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The switchable visible-light-mediated decarboxylative Heck-type reaction and oxo-alkylation reaction of N-hydroxyphthalimide esters under photocatalysis were developed. Disubstituted or trisubstituted alkenes were obtained in good yield with high E-select
- Xia, Zi-Hao,Zhang, Chun-Lin,Gao, Zhong-Hua,Ye, Song
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supporting information
p. 3496 - 3499
(2018/06/26)
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- Dual Functionalization of α-Monoboryl Carbanions through Deoxygenative Enolization with Carboxylic Acids
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A dual functionalization of 1,1-diborylalkanes through deoxygenative enolization with carboxylic acids was developed. 1,1-Diborylalkanes were activated by MeLi to generate α-monoboryl carbanions. In situ IR spectroscopy indicated an interaction between carboxylic acid and 1,1-diborylalkane before addition of the activation reagent. Release of the active α-monoboryl carbanion from the masked form was necessary for its reaction with carboxylate to afford enolate species. Electrophilic trapping of enolate species with various electrophiles achieved dual functionalization of 1,1-diborylalkanes to afford a variety of α-mono, di-, and tri-substituted ketones.
- Sun, Wei,Wang, Lu,Xia, Chungu,Liu, Chao
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supporting information
p. 5501 - 5505
(2018/04/09)
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- A preparation method of the organic compound (by machine translation)
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The invention relates to a preparation method of the organic compound: comprising the following steps: step one: in the nitrogen atmosphere, are added to the organic solvent in the organic carboxylic acid compound with the [...] compound; step two: to a mixture obtained in the step of adding alkyl lithium reagent, after reaction, is restored to the room temperature; step three: step b by heating the reaction mixture; step four: to step three by the electrophilic reagent is added in the mixture, to continue to reaction to obtain the ketone compound; wherein the organic carboxylic acid compound, alkyl lithium reagent, [...] compound and electrophilic reagents of the amount-of-substance ratio of 1.0: 2.5: 1.5: (1.0 - 2.0). The invention in a simple, economic, easy to obtain the raw material of the substrate, with only the addition of alkyl lithium as the activating agent, does not need any catalyst, a step to construct the previous method is difficult to efficient implementation of the ketone compound compound, such compound in the medical synthetic intermediates and organic photoelectric material science in very great application prospect. (by machine translation)
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Paragraph 0110; 0126
(2018/09/08)
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- Ligand-Controlled Chemoselective C(acyl)-O Bond vs C(aryl)-C Bond Activation of Aromatic Esters in Nickel Catalyzed C(sp2)-C(sp3) Cross-Couplings
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A ligand-controlled and site-selective nickel catalyzed Suzuki-Miyaura cross-coupling reaction with aromatic esters and alkyl organoboron reagents as coupling partners was developed. This methodology provides a facile route for C(sp2)-C(sp3) bond formation in a straightforward fashion by successful suppression of the undesired β-hydride elimination process. By simply switching the phosphorus ligand, the ester substrates are converted into the alkylated arenes and ketone products, respectively. The utility of this newly developed protocol was demonstrated by its wide substrate scope, broad functional group tolerance and application in the synthesis of key intermediates for the synthesis of bioactive compounds. DFT studies on the oxidative addition step helped rationalizing this intriguing reaction chemoselectivity: whereas nickel complexes with bidentate ligands favor the C(aryl)-C bond cleavage in the oxidative addition step leading to the alkylated product via a decarbonylative process, nickel complexes with monodentate phosphorus ligands favor activation of the C(acyl)-O bond, which later generates the ketone product.
- Chatupheeraphat, Adisak,Liao, Hsuan-Hung,Srimontree, Watchara,Guo, Lin,Minenkov, Yury,Poater, Albert,Cavallo, Luigi,Rueping, Magnus
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p. 3724 - 3735
(2018/03/21)
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- Switchable Selectivity in the Pd-Catalyzed Alkylative Cross-Coupling of Esters
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The Pd-catalyzed cross-coupling of phenyl esters and alkyl boranes is disclosed. Two reaction modes are rendered accessible in a selective fashion by interchange of the catalyst. With a Pd-NHC system, alkyl ketones can be prepared in good yields via a Suzuki-Miyaura reaction proceeding by activation of the C(acyl)-O bond. Use of a Pd-dcype catalyst enables alkylated arenes to be synthesized by a modified pathway with extrusion of CO. Applications of this divergent coupling strategy and the origin of the switchable selectivity are discussed.
- Masson-Makdissi, Jeanne,Vandavasi, Jaya Kishore,Newman, Stephen G.
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p. 4094 - 4098
(2018/07/15)
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- Palladium and visible-light mediated carbonylative Suzuki-Miyaura coupling of unactivated alkyl halides and aryl boronic acids
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Herein, a simple and efficient method for the palladium-catalyzed carbonylation of aryl boronic acids with unactivated alkyl iodides and bromides under visible-light irradiation, ambient temperature and low CO-pressure is presented. Notably, the procedure uses readily available equipment and an inexpensive palladium catalyst to generate the key alkyl radical intermediate. These mild conditions enabled the synthesis of a range of functionalized aryl alkyl ketones including the antipsychotic drug, melperone.
- Roslin, Sara,Odell, Luke R.
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supporting information
p. 6895 - 6898
(2017/07/10)
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- An increased understanding of enolate additions under mechanochemical conditions
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Very little is known about enolate addition chemistry under solver-free mechanochemical conditions. In this report, we investigated the ability to selectively form products arising from the primary, secondary, and tertiary enolates under solvent-free conditions. Using potassium tert-butoxide as the base and primary, secondary, and tertiary electrophiles, we were able to generate various enolate addition products including, 1,3,3,3-Tetraphenyl-2,2-dimethyl-1-propanone; a molecule we did not observe under traditional solution-based conditions.
- Hopgood, Heather,Mack, James
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- Triazolylidene Iron(II) Piano-Stool Complexes: Synthesis and Catalytic Hydrosilylation of Carbonyl Compounds
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A new series of iron(II) piano stool complexes was synthesized that contain monodentate triazolylidene ligands with different aryl and alkyl substituents as well as an example of a C,N-chelating pyridine-substituted triazolylidene iron complex. The electronic and steric effect of wingtip modification was assessed by electrochemical, infrared spectroscopic, and X-ray diffraction analysis. All complexes were active in the catalytic hydrosilylation of aldehydes and ketones. The monodentate systems outperform the chelating triazolylidene analogue by far, reaching turnover frequencies TOFmax as high as 14400 h-1 at 0.1 mol % catalyst loading. Mechanistic investigations indicate a radical mechanism for the catalytic H-Si bond activation.
- Johnson, Chloe,Albrecht, Martin
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p. 2902 - 2913
(2017/08/22)
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- Metal-Free Domino One-Pot Decarboxylative Cyclization of Cinnamic Acid Esters: Synthesis of Functionalized Indanes
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Trifluoroacetic acid promoted unprecedented domino reaction for the synthesis of diverse indanes starting from simple cinnamic acid esters is described. Their formation can be explained via acid triggered decarboxylation of cinnamic acid esters and subsequent inter/intramolecular cyclization. Overall process involves in the intramolecular cleavage of two σ-bonds (C-O and C-C) and inter/intramolecular construction of two/one C-C σ-bond(s). Significantly, this protocol was successful without the aid of any metal salts.
- Gopi Krishna Reddy, Alavala,Satyanarayana, Gedu
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p. 12212 - 12222
(2016/12/23)
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- Cu-Ag/hydrotalcite catalysts for dehydrogenative cross-coupling of primary and secondary benzylic alcohols
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The development of new and inexpensive heterogeneous catalysts for direct C-C cross-coupling of primary and secondary alcohols is a challenging goal and has great importance in academic and industrial sectors. In this work Cu-Ag/hydrotalcite (Cu-Ag/HT) catalysts were prepared and tested for their impact on this cross-coupling. The effect of supports, including MgO, γ-Al2O3 and HT with different Mg : Al molar ratios, was investigated. It was found that the acidic or basic properties of the supports affected product selectivity. The roles of Cu and Ag sites in the cross-coupling were also investigated with the prepared Cu-Ag/HT catalyst demonstrating high activity and selectivity for the reaction. The yield-to-target product of β-phenylpropiophenone reached 99% after 1 h under optimum reaction conditions. The stability in air and reusability studies show that Cu-Ag/HT can be stored for 6 days and can be used five times without apparent deactivation, respectively.
- Xu, Jin,Yue, Hongmei,Liu, Sheng,Wang, Hanfei,Du, Yuqun,Xu, Chunli,Dong, Wensheng,Liu, Chunling
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p. 24164 - 24174
(2016/03/15)
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- Oxidation and β-Alkylation of Alcohols Catalysed by Iridium(I) Complexes with Functionalised N-Heterocyclic Carbene Ligands
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The borrowing hydrogen methodology allows for the use of alcohols as alkylating agents for C-C bond forming processes offering significant environmental benefits over traditional approaches. Iridium(I)-cyclooctadiene complexes having a NHC ligand with a O- or N-functionalised wingtip efficiently catalysed the oxidation and β-alkylation of secondary alcohols with primary alcohols in the presence of a base. The cationic complex [Ir(NCCH3)(cod)(MeIm(2- methoxybenzyl))][BF4] (cod=1,5-cyclooctadiene, MeIm=1-methylimidazolyl) having a rigid O-functionalised wingtip, shows the best catalyst performance in the dehydrogenation of benzyl alcohol in acetone, with an initial turnover frequency (TOF0) of 1283 h-1, and also in the β-alkylation of 2-propanol with butan-1-ol, which gives a conversion of 94 % in 10 h with a selectivity of 99 % for heptan-2-ol. We have investigated the full reaction mechanism including the dehydrogenation, the cross-aldol condensation and the hydrogenation step by DFT calculations. Interestingly, these studies revealed the participation of the iridium catalyst in the key step leading to the formation of the new C-C bond that involves the reaction of an O-bound enolate generated in the basic medium with the electrophilic aldehyde.
- Jiménez, M. Victoria,Fernández-Tornos, Javier,Modrego, F. Javier,Pérez-Torrente, Jesús J.,Oro, Luis A.
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supporting information
p. 17877 - 17889
(2015/12/08)
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- A novel transition metal-free conjugate reduction of α,β-unsaturated ketones with tosylhydrazine as a hydrogen source
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A novel and efficient method has been developed for the chemoselective conjugate reduction of α,β-unsaturated ketones with tosylhydrazine as a hydrogen source to the corresponding saturated ketones in moderate to good yields. The present protocol does not require the use of transition metal, and is efficient being applicable to a wide range of substrates (25 examples).
- Zhou, Xiaomeng,Li, Xiaokang,Zhang, Wei,Chen, Junmin
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p. 5137 - 5140
(2015/02/19)
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- Structure-based design and synthesis of antiparasitic pyrrolopyrimidines targeting pteridine reductase 1
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The treatment of Human African trypanosomiasis remains a major unmet health need in sub-Saharan Africa. Approaches involving new molecular targets are important; pteridine reductase 1 (PTR1), an enzyme that reduces dihydrobiopterin in Trypanosoma spp., has been identified as a candidate target, and it has been shown previously that substituted pyrrolo[2,3-d]pyrimidines are inhibitors of PTR1 from Trypanosoma brucei (J. Med. Chem. 2010, 53, 221-229). In this study, 61 new pyrrolo[2,3-d]pyrimidines have been prepared, designed with input from new crystal structures of 23 of these compounds complexed with PTR1, and evaluated in screens for enzyme inhibitory activity against PTR1 and in vitro antitrypanosomal activity. Eight compounds were sufficiently active in both screens to take forward to in vivo evaluation. Thus, although evidence for trypanocidal activity in a stage I disease model in mice was obtained, the compounds were too toxic to mice for further development.
- Khalaf, Abedawn I.,Huggan, Judith K.,Suckling, Colin J.,Gibson, Colin L.,Stewart, Kirsten,Giordani, Federica,Barrett, Michael P.,Wong, Pui Ee,Barrack, Keri L.,Hunter, William N.
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p. 6479 - 6494
(2014/10/16)
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- C-C cross-coupling of primary and secondary benzylic alcohols using supported gold-based bimetallic catalysts
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Clean alcohol-alcohol cross-coupling: A clean and efficient one-pot direct C-C cross-coupling of equimolar amounts of primary and secondary alcohols by a facile hydrogen autotransfer pathway is achieved over a robust and easily recovered hydrotalcite-supported Au-Pd bimetallic catalyst system. A variety of primary and secondary alcohols have been selectively converted into the corresponding b-alkylated ketones in good yields.
- Liu, Xiang,Ding, Ran-Sheng,He, Lin,Liu, Yong-Mei,Cao, Yong,He, He-Yong,Fan, Kang-Nian
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p. 604 - 608
(2013/07/27)
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- An Efficient α-alkylation of aromatic ketones with primary alcohols catalyzed by [cp*ircl2]2 without solvent
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Aromatic ketones are directly alkylated at α position with primary alcohols at 110°C in the presence of catalytic amount of KOH and [Cp*IrCl2]2 (Cp=pentamethylcyclopentadienyl) catalyst. The reaction is carried out in the absence of any solvent or additive, which generates only water as the byproduct in theory. It is very efficient and generally completed in 10 min in good isolated yields. The reaction is believed to undergo successive hydrogen transfer and cross aldol condensation processes. Copyright
- Li, Jian,Zhang, Weixing,Wang, Feng,Jiang, Min,Dong, Xiaochun,Zhao, Weili
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p. 2363 - 2366,4
(2020/09/16)
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- Copper-catalyzed oxaziridine-mediated oxidation of C-H bonds
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The highly regio- and chemoselective oxidation of activated C-H bonds has been observed via copper-catalyzed reactions of oxaziridines. The oxidation proceeded with a variety of substrates, primarily comprising allylic and benzylic examples, as well as one example of an otherwise unactivated tertiary C-H bond. The mechanism of the reaction is proposed to involve single-electron transfer to the oxaziridines to generate a copper-bound radical anion, followed by hydrogen atom abstraction and collapse to products, with regeneration of the catalyst by a final single-electron transfer event. The involvement of allylic radical intermediates was supported by a radical-trapping experiment with TEMPO.
- Motiwala, Hashim F.,Guelgeze, Belgin,Aube, Jeffrey
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p. 7005 - 7022
(2012/10/08)
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- Ligand-accelerated Pd-catalyzed ketone γ-arylation via C-C cleavage with aryl chlorides
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A highly efficient Pd-catalyzed arylative ring expansion of cyclobutanols via C-C bond cleavage is presented. The method allows the coupling of aryl chlorides at low catalyst loadings with a wide range of functional groups and substitution patterns, thus constituting a straightforward alternative for preparing rather elusive γ-arylated ketones.
- Ziadi, Asraa,Martin, Ruben
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supporting information; experimental part
p. 1266 - 1269
(2012/04/23)
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- Iridium phosphine abnormal N-heterocyclic carbene complexes in catalytic hydrogen transfer reactions
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Several iridium complexes bearing chelating abnormal N-heterocyclic carbenes (NHCs) are shown to be active catalysts for transfer hydrogenation of ketones or enones, dehydrative C-C coupling between primary and secondary alcohols, and dehydrogenation of benzyl alcohol to benzyl benzoate. In the transfer hydrogenation of acetophenone, abnormal NHC complexes give higher activity than a normal analogue. Dehydrative C-C coupling reactions between primary and secondary alcohols result in β-alkylation of the secondary alcohols, using primary alcohols as the apparent alkylating reagents, and such reactions proceed with high yield and selectivity. These catalytic processes are known to involve metal-mediated temporary borrowing of hydrogen from alcohols and subsequent delivery of the hydrogen to CC and /or CO bonds.
- Gong, Xue,Zhang, Hong,Li, Xingwei
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supporting information; experimental part
p. 5596 - 5600
(2011/11/06)
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- Synthesis of ketones by palladium-catalysed desulfitative reaction of arylsulfinic acids with nitriles
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Palladium-catalysed desulfitative addition of arylsulfinic acids to aryl and alkyl nitriles with 2,2′-bipyridine as a ligand afforded a variety of aryl ketones via hydrolysis of ketimine intermediates.
- Miao, Tao,Wang, Guan-Wu
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supporting information; experimental part
p. 9501 - 9503
(2011/10/01)
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- Inter- and intramolecular hydroacylation of alkenes employing a bifunctional catalyst system
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Based on a conceptually innovative bifunctional P,N ligand, an efficient protocol for the rhodium-catalyzed inter- and intramolecular hydroacylation of alkenes has been developed.
- Vautravers, Nicolas R.,Regent, Damien D.,Breit, Bernhard
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supporting information; experimental part
p. 6635 - 6637
(2011/06/27)
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- Titanocene(III) chloride mediated reductive cleavage of arylcyclopropyl ketones
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Titanocene(III) chloride (Cp2TiCl) mediated cleavage of arylcyclopropyl ketones has been accomplished. Both saturated and β-H eliminated unsaturated aromatic compounds are formed in different ratio depending on the substrate. Ti(III) species has been prepared in situ from commercially available titanocene dichloride (Cp2TiCl2) and zinc dust in THF.
- Paira,Mandal,Roy
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experimental part
p. 573 - 577
(2010/12/25)
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- Synthesis of 1-phenylbut-3-ene-1,2-dione and its attempted radical polymerization
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1,2-Diketone moiety-bearing monomer 1-phenylbut-3-ene-1,2-dione, an analogue of phenyl vinyl ketone, was synthesized from 4-chlorobutyryl chloride in a 29 % overall yield in five steps. Following acylation of benzene with 4-chlorobutyryl chloride, the resulting α-methylene group was oxidized to 1,2-diketone in three steps: successive bromination, substitution with lithium hydroxide, and oxidation of α-hydroxyketone with potassium dichromate. The final step was dehydrochlorination of 4-chloro-1-phenyl-butane-1,2-dione. The attempted copolymerization of this monomer with styrene, using AIBN as the initiator, was unsuccessful.
- Husar, Branislav,Lukac, Ivan,Chmela, Stefan,Canet, Jean-Louis,Troin, Yves
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experimental part
p. 499 - 503
(2011/11/06)
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