- Novelmeta-benzothiazole and benzimidazole functionalised POCOP-Ni(ii) pincer complexes as efficient catalysts in the production of diarylketones
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The synthesis of four novel non-symmetric Ni(ii)-POCOP pincer complexesmeta-functionalized with either benzothiazole or benzimidazole at the central aryl ring is described. All complexes were fully characterised in solution by various analytical techniques and the molecular structures in the solid state of complexes1b,2aand2bwere unequivocally determined by single crystal X-ray diffraction analysis. In addition, the Ni(ii)-POCOP pincer complexes were efficiently used as catalysts in the synthesis of diarylketones by cross-coupling reactions of functionalized benzaldehydes and boronic acid derivatives under relatively mild conditions. An important aspect of this transformation is the dependence on the steric properties of the donor groups (OPR2) of the pincer ligands, the more active compounds having the phosphinitos bearing isopropyl groups (1aand2a) than those containingtert-butyl substituents (1band2b).
- Castillo-García, Antonio A.,González-Sebastián, Lucero,Lomas-Romero, Leticia,Hernandez-Ortega, Simon,Toscano, Ruben A.,Morales-Morales, David
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p. 10204 - 10216
(2021/06/18)
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- A Bifunctional Iron Nanocomposite Catalyst for Efficient Oxidation of Alkenes to Ketones and 1,2-Diketones
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We herein report the fabrication of a bifunctional iron nanocomposite catalyst, in which two catalytically active sites of Fe-Nx and Fe phosphate, as oxidation and Lewis acid sites, were simultaneously integrated into a hierarchical N,P-dual doped porous carbon. As a bifunctional catalyst, it exhibited high efficiency for direct oxidative cleavage of alkenes into ketones or their oxidation into 1,2-diketones with a broad substrate scope and high functional group tolerance using TBHP as the oxidant in water under mild reaction conditions. Furthermore, it could be easily recovered for successive recycling without appreciable loss of activity. Mechanistic studies disclose that the direct oxidation of alkenes proceeds via the formation of an epoxide as intermediate followed by either acid-catalyzed Meinwald rearrangement to give ketones with one carbon shorter or nucleophilic ring-opening to generate 1,2-diketones in a cascade manner. This study not only opens up a fancy pathway in the rational design of Fe-N-C catalysts but also offers a simple and efficient method for accessing industrially important ketones and 1,2-diketones from alkenes in a cost-effective and environmentally benign fashion.
- Ma, Zhiming,Ren, Peng,Song, Tao,Xiao, Jianliang,Yang, Yong,Yuan, Youzhu
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p. 4617 - 4629
(2020/05/19)
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- Acyl radicals from α-keto acids using a carbonyl photocatalyst: Photoredox-catalyzed synthesis of ketones
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Acyl radicals have been generated from α-keto acids using inexpensive and commercially available 2-chloro-thioxanthen-9-one as the photoredox catalyst under visible light illumination. These reactive species added to olefins or coupled with aryl halides via a bipyridylstabilized Ni(II) catalyst, enabling easy access to a diverse range of ketones. This reliable, atom-economical, and eco-friendly protocol is compatible with a wide range of functional groups.
- Zhu, Da-Liang,Wu, Qi,Young, David James,Wang, Hao,Ren, Zhi-Gang,Li, Hong-Xi
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supporting information
p. 6832 - 6837
(2020/10/12)
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- Synthesis of biaryl ketones by arylation of Weinreb amides with functionalized Grignard reagents under thermodynamic controlvs.kinetic control ofN,N-Boc2-amides
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A highly efficient method for chemoselective synthesis of biaryl ketones by arylation of Weinreb amides (N-methoxy-N-methylamides) with functionalized Grignard reagents is reported. This protocol offers rapid entry to functionalized biaryl ketones after Mg/halide exchange with i-PrMgCl·LiCl under operationally-simple and practical reaction conditions. The scope of the method is highlighted in >40 examples, including bioactive compounds and pharmaceutical derivatives. Collectively, this transition-metal-free approach offers a major advantage over the recently established cross-coupling of amides by oxidative addition of N-C(O) bonds. Considering the utility of amide acylation reactions in modern synthesis, we expect that this method will be of broad interest.
- Li, Guangchen,Szostak, Michal
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supporting information
p. 3827 - 3831
(2020/06/03)
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- Kinetically Controlled, Highly Chemoselective Acylation of Functionalized Grignard Reagents with Amides by N?C Cleavage
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The direct transition-metal-free acylation of amides with functionalized Grignard reagents by highly chemoselective N?C cleavage under kinetic control has been accomplished. The method offers rapid and convergent access to functionalized biaryl ketones through transient tetrahedral intermediates. The direct access to functionalized Grignard reagents by in situ halogen–magnesium exchange promoted by the versatile turbo-Grignard reagent (iPrMgCl?LiCl) permits excellent substrate scope with respect to both the amide and Grignard coupling partners. These reactions enable facile, operationally simple and chemoselective access to tetrahedral intermediates from amides under significantly milder conditions than chelation-controlled intermediates. This novel direct two-component coupling sets the stage for using amides as acylating reagents in an alternative paradigm to the metal-chelated approach, acyl metals and Weinreb amides.
- Li, Guangchen,Szostak, Michal
-
supporting information
p. 611 - 615
(2020/01/02)
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- Polymer-incarcerated palladium-catalyzed facile: In situ carbonylation for the synthesis of aryl aldehydes and diaryl ketones using CO surrogates under ambient conditions
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In this existing work, an efficient polymer-supported palladium catalyst, a furfurylamine-functionalized Merrifield complex of palladium [Pd@(Merf-FA)], was synthesized and characterized, showing excellent catalytic activity towards in situ carbonylation reactions using carbon monoxide surrogates like formic acid and chloroform. Herein, we examined the catalytic activity of the Pd@(Merf-FA) catalyst for the formylation of aryl iodides and carbonylative Suzuki-Miyaura coupling reactions. The Pd@(Merf-FA) catalyst was systematically characterized by several techniques like HRTEM, elemental mapping, PXRD, TGA-DTA, FESEM, UV-vis, EDAX, CHN and AAS analysis. The catalyst is highly recyclable, able to be recycled up to six times without showing any significant decrease in catalytic activity. The [Pd@(Merf-FA)] catalyst proved to be more efficient compared to the corresponding homogeneous palladium catalyst. In addition, the leaching experiment of the synthesized catalyst was studied, which showed that negligible leaching of metal occurred from the polymeric support.
- Dey, Tusar Kanto,Basu, Priyanka,Riyajuddin, Sk,Ghosh, Aniruddha,Ghosh, Kaushik,Manirul Islam, Sk
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p. 9802 - 9814
(2019/07/04)
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- Synthesis of some ketones via nano-nickel oxide catalyzed acylation of arylzinc reagents; strategy involving the use of mixed (methyl)(aryl)zincs
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Nano-NiO catalyzed acylation of mixed (methyl)(aryl)zincs with aromatic acyl halides in THF at room temperature provides a new facile route for aryl–aroyl coupling. Among NiCl2 .L2 and NiCl2 .L (L = monodentate and bidentate phosphine ligand) catalysts, the lower catalyst loading of NiCl2 (dppf) may seem attractive; however, nano-NiO, being the lowest cost catalyst, is more favorable for aroylation of (methyl)(aryl)zincs. This procedure also provides a supplement to Cu and Pd catalyzed acylation of diorganozincs.
- Pekel, ?zgen ?MüR,Erdik, Ender,Kalkan, Melike
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p. 759 - 767
(2018/06/07)
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- CO2-Catalyzed oxidation of benzylic and allylic alcohols with DMSO
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CO2-catalyzed transition-metal-free oxidation of alcohols has been achieved. Earlier, several methodologies have been explored for alcohol oxidations based on transition-metal catalysts. However, owing to the cheaper price, easy separation and nontoxicity, transition-metal-free systems are in high demand to the pharmaceutical industries. For this reason, various primary and secondary alcohols have been selectively oxidized to the corresponding carbonyl compounds using CO2 as a catalyst in the presence of different functional groups such as nitrile, nitro, aldehyde, ester, halogen, ether, and so on. At the end, transition-metal-free syntheses of pharmaceuticals have also been achieved. Finally, the role of CO2 has been investigated in detail, and the mechanism is proposed on the basis of experiments and DFT calculations.
- Riemer, Daniel,Mandaviya, Bhavdip,Schilling, Waldemar,G?tz, Anne Charlotte,Kühl, Torben,Finger, Markus,Das, Shoubhik
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p. 3030 - 3034
(2018/04/14)
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- Palladium-Catalyzed Ligand-Free Decarboxylative Coupling of α- Oxocarboxylic Acid with Aryl Diazonium Tetrafluoroborate: An Access to Unsymmetrical Diaryl Ketones
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Diaryl ketones are of much importance in organic synthesis as versatile intermediates and in industry for their useful properties. A mild and efficient palladium-catalyzed traditional ligand-free decarboxylative coupling of aryl α-keto carboxylic acid with aryl diazonium fluoroborate has been developed. A series of unsymmetrical diaryl ketones has been synthesized in moderate to good yields using this procedure. A radical pathway involving the acyl radical has been suggested.
- Panja, Subir,Maity, Pintu,Ranu, Brindaban C.
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p. 12609 - 12618
(2018/10/20)
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- Synthesis and architecture of polystyrene-supported Schiff base-palladium complex: Catalytic features and functions in diaryl urea preparation in conjunction with Suzuki-Miyaura cross-coupling reaction by reductive carbonylation
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This work represents an efficient and unique phosphine-free approach for the polystyrene embedded Schiff-base palladium catalyzed diaryl urea synthesis and Suzuki-Miyaura cross-coupling reaction by reductive carbonylation process. The careful instrumental investigations with FE-SEM, TEM, EDAX, TGA, UV–Vis, FTIR, AAS, and elemental analysis precisely characterized the developed heterogeneous catalyst. Reaction parameters, like catalytic natures, starting materials, reaction environment, and solvent were examined sequentially. The present work has been adequately addressed to account for the generation and characterization of a new polymer bound Pd-catalyst and using it in the synthesis of diaryl ureas and diaryl ketones, with no substantial decay of catalytic activity.
- Basu, Priyanka,Riyajuddin, Sk,Dey, Tusar Kanto,Ghosh, Aniruddha,Ghosh, Kaushik,Islam, Sk Manirul
-
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- Acyl and Decarbonylative Suzuki Coupling of N-Acetyl Amides: Electronic Tuning of Twisted, Acyclic Amides in Catalytic Carbon-Nitrogen Bond Cleavage
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We report the Pd-catalyzed acyl and the Ni-catalyzed biaryl Suzuki-Miyaura cross-coupling of N-acetyl-amides with arylboronic acids by selective N-C(O) cleavage. Activation of the amide bond by N-acylation provides electronically destabilized, acyclic, nonplanar amide, which readily undergoes cross-coupling with a wide range of boronic acids to produce biaryl ketones or biaryls in a highly efficient manner. Most crucially, the presented results introduce N-acetyl-amides as reactive acyclic amides in the emerging manifold of transition-metal-catalyzed amide cross-coupling. The scope and origin of high selectivity are discussed. Mechanistic studies point to remodeling of amidic resonance and amide bond twist as selectivity determining features in a unified strategy for cross-coupling of acyclic amides. Structural studies, mechanistic investigations as well as beneficial effects of the N-acyl substitution on cross-coupling of amides are reported.
- Liu, Chengwei,Li, Guangchen,Shi, Shicheng,Meng, Guangrong,Lalancette, Roger,Szostak, Roman,Szostak, Michal
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p. 9131 - 9139
(2018/09/21)
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- Nickel-Catalyzed C-CN Bond Formation via Decarbonylative Cyanation of Esters, Amides, and Intramolecular Recombination Fragment Coupling of Acyl Cyanides
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An efficient nickel-catalyzed decarbonylative cyanation reaction which allows the direct functional-group interconversion of readily available esters into the corresponding nitriles was developed. This reaction successfully offers access to structurally diverse nitriles with high efficiency and excellent functional-group tolerance and provides a good alternative to classical synthetic pathways from diazonium salts or organic halide compounds.
- Chatupheeraphat, Adisak,Liao, Hsuan-Hung,Lee, Shao-Chi,Rueping, Magnus
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supporting information
p. 4255 - 4258
(2017/08/23)
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- One pot synthesis of unsymmetrical ketones from carboxylic and boronic acids via PyClU-mediated acylative Suzuki coupling
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A synthetic procedure for the preparation of ketones from easily accessible carboxylic acids has been developed. This methodology proceeds via in situ activation of the carboxylic acid with PyClU, followed by the palladium-catalyzed acylative cross-coupling with boronic acids. The reaction is performed in one pot, without the need of phosphine ligands, at room temperature and in reaction times of 2 h or less. The scope of the reaction is robust with aryl boronic and carboxylic acids.
- Garcia-Barrantes, Pedro M.,McGowan, Kevin,Ingram, Steven W.,Lindsley, Craig W.
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p. 898 - 901
(2017/02/10)
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- Chemoselective generation of acyl phosphates, acylium ion equivalents, from carboxylic acids and an organophosphate ester in the presence of a Br?nsted acid
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We describe the chemoselective conversion of carboxylic acids to functional aromatic ketones promoted by a tailored organophosphate ester in the presence of a Br?nsted acid. The protonated phosphate ester reacts with the carboxylic acid to form acyl phosphate, which reacts with benzenes to give aromatic ketones, probably through the acylium ion or its equivalent. The reaction time is short even at room temperature, and the reaction is compatible with various other functional groups, including amines, olefins, esters, amides and nitriles.
- Sumita, Akinari,Otani, Yuko,Ohwada, Tomohiko
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supporting information
p. 1482 - 1485
(2017/02/05)
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- Palladium-catalyzed Suzuki-Miyaura coupling of amides by carbon-nitrogen cleavage: General strategy for amide N-C bond activation
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The first palladium-catalyzed Suzuki-Miyaura cross-coupling of amides with boronic acids for the synthesis of ketones by sterically-controlled N-C bond activation is reported. The transformation is characterized by operational simplicity using bench-stable, commercial reagents and catalysts, and a broad substrate scope, including substrates with electron-donating and withdrawing groups on both coupling partners, steric-hindrance, heterocycles, halides, esters and ketones. The scope and limitations are presented in the synthesis of >60 functionalized ketones. Mechanistic studies provide insight into the catalytic cycle of the cross-coupling, including the first experimental evidence for Pd insertion into the amide N-C bond. The synthetic utility is showcased by a gram-scale cross-coupling and cross-coupling at room temperature. Most importantly, this process provides a blueprint for the development of a plethora of metal catalyzed reactions of typically inert amide bonds via acyl-metal intermediates. A unified strategy for amide bond activation to enable metal insertion into N-C amide bond is outlined (Scheme 1).
- Meng, Guangrong,Szostak, Michal
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p. 5690 - 5707
(2016/07/06)
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- Rhodium-catalyzed synthesis of aryl ketones from carboxylic acid anhydrides and potassium aryltrifluoroborates in the presence of CuI
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A new rhodium-catalyzed cross-coupling of carboxylic acid anhydrides and potassium aryltrifluoroborates was described. In this system CuI played a very important role. Various functionalities were compatible in the reaction, and the desired products were obtained in good to excellent yields. A mechanism of this reaction using a Rh(I) model catalyst have also been proposed.
- Liu, Xia,Yi, Ze,Yi, Maocong,Wang, Jianhui,Liu, Guiyan
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p. 4635 - 4639
(2015/06/08)
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- Synthesis of biarylketones and phthalides from organoboronic acids and aldehydes catalyzed by cobalt complexes
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A cobalt-catalyzed addition of aryl- and alkenylboronic acids to aldehydes and phthalaldehyde to give the corresponding biarylketones and 3-aryl phthalides in good to excellent yields in one pot is described.
- Karthikeyan, Jaganathan,Parthasarathy, Kanniyappan,Cheng, Chien-Hong
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supporting information; experimental part
p. 10461 - 10463
(2011/11/06)
-
- Na-promoted aerobic oxidation of alcohols to ketones
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Aerobic oxidation of a number of diaryl and arylalkyl carbinols to ketones was promoted by Na in THF at room temperature with up to 99% yield. This new oxidation method is also selective with good efficiency for the oxidation of benzylic secondary alcohols but not for a primary alcohol or nonbenzylic secondary alcohols. Under nitrogen, a catalytic amount of Ni or transition metal halides such as CoCl3, FeCl3, and NiCl3 in combination with Na was also found to conduct a dehydrogenation of a secondary alcohol to the corresponding ketone in high yield at room temperature.
- Zhou, Li-Hong,Yu, Xiao-Qi,Pu, Lin
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scheme or table
p. 475 - 477
(2010/09/20)
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- Carbomylative Suzuki-Miyaura coupling of arylboronic acids with aryl iodides catalyzed by the MCM-41-supported bidentate phosphane palladium(II) complex
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The first heterogeneous carbonylative Suzuki-Miyaura cross-coupling reaction of arylboronic acids with aryl iodides under an atmospheric pressure of carbon monoxide has been achieved in anisole at, 80 °C in the presence of a catalytic amount of an MCM-41-supported bidentate phosphane palladium(II) complex (MCM-41-2P-PdII), yielding unsymmetrical biaryl ketones in good-to-high yields. This polymeric palladium catalyst exhibited higher activity and selectivity than fPdCl2(PPh3)2] and can be reused at least 10 times without any decrease in activity. Wiley-VCH Verlag GmbH & Co, KGaA.
- Cai, Mingzhong,Zheng, Guomin,Zha, Lingfang,Peng, Jian
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experimental part
p. 1585 - 1591
(2009/09/08)
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- Selective generation of lithiated benzonitriles: The importance of reaction conditions
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(Chemical Equation Presented) Lithiated benzonitriles can be generated in high yields from reactions of bromobenzonitriles with n-BuLi in THF under standard cryogenic conditions (ca. -70°C) provided the reverse addition mode is employed. The resultant ary
- Lulinski, Sergiusz,Zajac, Katarzyna
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p. 7785 - 7788
(2008/12/22)
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- Palladium-phosphinous acid-catalyzed cross-coupling of aryl and acyl halides with aryl-, alkyl-, and vinylzinc reagents
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(Chemical Equation Presented) Several palladium-phosphinous acids have been prepared and employed in cross-coupling reactions of aryl or acyl halides with aliphatic and aromatic organozinc reagents. The POPd7-catalyzed reaction of aryl halides, including electron-rich aryl chlorides, and arylzinc reagents was found to afford biaryls exhibiting alkoxy, alkylthio, amino, ketone, cyano, nitro, ester, and heteroaryl groups in 75-93% yield. Excellent results were obtained with sterically hindered substrates which gave di- and tri-ortho-substituted biaryls in up to 92% yield. Aryl halides also undergo POPd7-catalyzed aryl-vinyl and aryl-alkyl bond formation under mild conditions. Styrenes and alkylarenes were prepared in 79-93% yield from aryl halides and vinyl or alkylzinc reagents. The replacement of aryl halides by acyl halides provides access to ketones which were produced in up to 98% yield when POPd was used as catalyst. This approach overcomes the limited substrate scope, reduced regiocontrol, and low functional group tolerance of traditional Friedel-Crafts acylation methods.
- Xu, Hanhui,Ekoue-Kovi, Kekeli,Wolf, Christian
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p. 7638 - 7650
(2008/12/22)
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- Efficient synthesis of functionalized organozinc compounds by the direct insertion of zinc into organic iodides and bromides
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(Chemical Equation Presented) Insider dealing: A wide range of poly-functional (hetero)aromatic and aliphatic zinc reagents can be easily prepared in THF. The compounds are formed by a Zn insertion reaction mediated by the addition of LiCl (see scheme; All = allyl).
- Krasovskiy, Arkady,Malakhov, Vladimir,Gavryushin, Andrei,Knochel, Paul
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p. 6040 - 6044
(2007/10/03)
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- Substituted 4,5-dihydro-1,2,4-triazin-6-ones, 1,2,4-triazin-6-ones, and their use as fungicides
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This invention relates to substituted dihydrotriazinones, triazinones and related compounds, compositions comprising such compounds and an agronomically acceptable carrier, and the use thereof as broad spectrum fungicides. This invention also teaches methods of preparing these compounds as well as methods of using the compounds as fungicides.
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- Method of preparing organomagnesium compounds
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The present invention is directed to a reagent for use in the preparation of organomagnesium compounds as well as to a method of preparing such organomagnesium compounds. The present invention furthermore provides a method of preparing functionalized or unfunctionalized organic compounds as well as the use of the reagents of the present invention in the preparation of organometallic compounds and their reaction with electrophiles. Finally, the present invention is directed to the use of lithium salts - LiY in the preparation of organometallic compounds and their reactions with electrophiles and to an organometallic compound which is obtainable by the disclosed method.
- -
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Page/Page column 13
(2010/02/14)
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- Preparation and Reactions of Polyfunctional Magnesium Arylcuprates Obtained by an Iodine-Copper Exchange
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The preparation of polyfunctional magnesium cuprates of type 1 can be achieved via an iodine-copper exchange reaction using the cyclic magnesium cuprate 3. A range of functional groups like an ester, halide (F, Br), nitrile or even a ketone can be tolerated. The new cuprates can be acylated and allylated in good yields leading to a range of polyfunctional products.
- Yang, Xiaoyin,Knochel, Paul
-
-
- A LiCl-mediated Br/Mg exchange reaction for the preparation of functionalized aryl- and heteroarylmagnesium compounds from organic bromides
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A wide range of aryl and heteroaryl bromides, which are usually sluggish in exchange reactions, are readily converted into the corresponding Grignard reagents by means of a Br/Mg exchange reaction triggered by iPrMgCl·LiCl (see scheme). These Grignard intermediates react with electrophiles in good yields.
- Krasovskiy, Arkady,Knochel, Paul
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p. 3333 - 3336
(2007/10/03)
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- A convenient method for the preparation of aromatic ketones from acyl chlorides and arylzinc bromides using a cobalt catalysis
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Aromatic ketones are synthesized efficiently via cobalt catalyzed cross-coupling reaction between arylzinc bromides and acid chlorides. Arylzinc bromides prepared chemically via a cobalt catalysis undergo coupling without additional catalyst unlike their electrochemical analogs.
- Fillon, Hyacinthe,Gosmini, Corinne,Périchon, Jacques
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p. 8199 - 8202
(2007/10/03)
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- Palladium-catalyzed synthesis of aryl ketones from boronic acids and carboxylic acids activated in situ by pivalic anhydride
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A new palladium-catalyzed cross-coupling reaction between arylboronic acids and mixed anhydrides, generated in situ from carboxylic acids and pivalic anhydride, is presented. Optimization of the new catalyst and the reaction conditions led to the development of a convenient one-pot ketone synthesis directly from carboxylic and boronic acids in the presence of different (phosphane)palladium complexes in wet THF at 60 °C. Systematic studies were performed to elucidate the reaction mechanism of this transformation. The scope and the limitations of the new process are demonstrated by the synthesis of 33 functionalized ketones. Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002.
- Goossen, Lukas J.,Ghosh, Keya
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p. 3254 - 3267
(2007/10/03)
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- A new practical ketone synthesis directly from carboxylic acids: First application of coupling reagents in palladium catalysis
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A new palladium-catalyzed cross-coupling reaction between arylboronic acids and carboxylic acids, activated in situ for the oxidative addition to a tricyclohexylphosphine palladium(0) catalyst by treatment with di(N-succinimidyl) carbonate (DSC) is disclosed, which allows the high-yielding synthesis of various functionalized arylketones under mild conditions.
- Goossen,Ghosh
-
p. 2084 - 2085
(2007/10/03)
-
- Direct Formation and Reaction of Thienyl-Based Organocopper Reagents
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The preparation of a highly reactive zerovalent copper complex by the direct reduction of lithium (2-thienylcyano)cuprate with preformed lithium naphthalenide is described.This active copper species oxidatively adds to carbon-halogen bonds to form organocopper reagents.The ability to directly form the organocopper reagent from organic halides and active copper allows for the incorporation of a wide variety of functionalities to be present in the organic halides and the organocopper reagents.Significantly, this formulation of active copper was able to oxidatively add to allyl chlorides and acetates at low temperatures to allow the direct formation of allylic organocopper reagents without Wurtz-type homocoupling.These functionalized organocopper compounds are able to undergo a variety of reactions, such as cross-coupling with acid chlorides, 1,4-conjugate addition with α,β-unsaturated carbonyl compounds, and intermolecular and intramolecular epoxide-opening reactions.Subsequently, this copper species avoids the use of phosphine ligands affording the product isolation much more convenient than with phosphine-based organocopper reagents.
- Rieke, Reuben D.,Klein, Walter R.,Wu, Tse-Chong
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p. 2492 - 2500
(2007/10/02)
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- DIRECT FORMATION AND REACTION OF FUNCTIONALIZED THIENYL-BASED ORGANOCOPPER REAGENTS
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Highly reactive copper solutions have been prepared by the direct reduction of lithium 2-thienylcyanocuprate.Product isolation was much easier using the thienyl-based organocopper reagents as opposed to phosphine-based organocopper reagents
- Rieke, Reuben D.,Wu, Tse-Chong,Stinn, Dean E.,Wehmeyer, Richard M.
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p. 1833 - 1840
(2007/10/02)
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- Deactivation of Triplet Phenyl Alkyl Ketones by Conjugatively Electron-Withdrawing Substituents
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Para-cyano, -carbomethoxy, and -acyl substituents decrease the triplet reactivity of valerophenone (γ-hydrogen abstraction), whereas comparable meta substituents increase reactivity.Spectroscopic results are presented which indicate that para-(-R) substituents lower ?,?* triplet energies so much more than n,?* energies that the lowest triplets become largely ?,?* in nature.Meta-(-R) substituents do not stabilize ?,?* triplets enough to invert triplet levels.Both substitution patterns support a largely 1,4-biradical structure for the lowest ?,?* triplet of acylbenzenes.Ortho substituents show the usual steric anomalies: ortho cyano enhances valerophenone triplet reactivity by stabilizing the n,?* triplet; ortho carbomethoxy deactivates valerophenone by stabilizing the ?,?* triplet but not the n,?.*
- Wagner, Peter J.,Siebert, Elizabeth J.
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p. 7329 - 7335
(2007/10/02)
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- Merostabilization in radical ions, triplets, and biradicals. 4. Substituent effects on the half-wave reduction potentials and n, ?* triplet energies of aromatic ketones
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The half-wave reduction potentials, measured by cyclic voltammetry, and n, ?* triplet energies, measured by phosphorescence spectroscopy, were determined for a series of eighteen symmetrically and unsymmetrically substituted benzophenones.Attempts are made to correlate the results with Hammett substituent constants.Better correlations are observed when the data are correlated with a two-parameter function consisting of Hammett substituent constants and a set of substituent parameters describing variations in free radical stability.Significant deviations from "normal" behaviour are observed for benzophenones substituted by both electron-donating and electron-withdrawing substituents.These deviations are attributed to merostabilization of the radical-like species, and an empirical approach designed to evaluate the importance of this effect is developed.Ab initio calculations of molecular orbital energies in meta- and para-substituted benzaldehydes are used to evaluate the substituent effects on E1/2red and ETn,?* in terms of the effect on the energies of the n- and ?*-orbitals.
- Leigh, William J.,Arnold, Donald R.,Humphreys, Robert W. R.,Wong, Po Cheong
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p. 2537 - 2549
(2007/10/02)
-