- Highly efficient synthesis of 1,2-disubstituted acetylenes derivatives from the cross-coupling reactions of 1-bromoalkynes with organotitanium reagents
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A Highly efficient route for the synthesis of 1,2-disubstituted acetylene derivatives has been developed by nickel catalyzed cross-couplings of alkynyl halides with aryl titanium reagents under mild conditions. This has given corresponding cross-coupling products good to excellent isolated yields of up to 92 %. The aryls bearing electron-donating or electron-withdrawing groups in either alkynylhalides or aryltitanium substrates gave cross-coupling products good yields. This process was simple and easily performed, which provides an efficient method for the synthesis of 1,2-disubstituted acetylenes derivatives.
- Li, Qing-Han,Wu, Chuan
-
supporting information
(2021/08/25)
-
- Decarbonylative Sonogashira Cross-Coupling of Carboxylic Acids
-
Decarbonylative Sonogashira cross-coupling of carboxylic acids by palladium catalysis is presented. The carboxylic acid is activated in situ by the formation of a mixed anhydride and further decarbonylates using the Pd(OAc)2/Xantphos system to provide an aryl-Pd intermediate, which is intercepted by alkynes to access the traditional Pd(0)/(II) cycle using carboxylic acids as ubiquitous and orthogonal electrophilic cross-coupling partners. The methodology efficiently constructs new C(sp2)-C(sp) bonds and can be applied to the derivatization of pharmaceuticals. Mechanistic studies give support to decarbonylation preceding transmetalation in this process.
- Liu, Chengwei,Szostak, Michal
-
supporting information
p. 4726 - 4730
(2021/06/28)
-
- Facile one-pot synthesis of diarylacetylenes from arylaldehydes: Via an addition-double elimination process
-
A practical one-pot protocol has been developed to synthesize diarylacetylenes from arylaldehydes by treatment with 1-(arylmethyl)benzotriazoles and LiN(SiMe3)2. The reaction proceeded through imine formation, Mannich-type addition and double elimination to deliver products in up to 99% yields with broad substrate scope. In addition, gram-scale synthesis of 1-bromo-4-(phenylethynyl)benzene has been demonstrated.
- Chen, Jianyang,Zhang, Xuan,Wu, Jiajun,Wang, Rui,Lei, Chunlin,An, Yanan
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p. 4701 - 4705
(2021/06/11)
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- Copper(0) nanoparticle catalyzed Z-Selective Transfer Semihydrogenation of Internal Alkynes
-
The use of copper(0) nanoparticles in the transfer semihydrogenation of alkynes has been investigated as a lead-free alternative to Lindlar catalysts. A stereo-selective methodology for the hydrogenation of internal alkynes to the corresponding (Z)-alkenes in high isolated yields (86% average) has been developed. This green and sustainable transfer hydrogenation protocol relies on non-noble copper nanoparticles for reduction of both electron-rich and electron-deficient, aliphatic-substituted and aromatic- substituted internal alkynes. Polyols, such as ethylene glycol and glycerol, have been proven to act as hydrogen sources, and excellent stereo- and chemoselectivity have been observed. Enabling technologies, such as microwave and ultrasound irradiation are shown to enhance heat and mass transfer, whether used alone or in combination, resulting in a decrease in reaction time from hours to minutes. (Figure presented.).
- Moran, Maria Jesus,Martina, Katia,Bieliunas, Vidmantas,Baricco, Francesca,Tagliapietra, Silvia,Berlier, Gloria,De Borggraeve, Wim M.,Cravotto, Giancarlo
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supporting information
p. 2850 - 2860
(2021/05/06)
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- Ligand-Promoted Alkynylation of Aryl Ketones: A Practical Tool for Structural Diversity in Drugs and Natural Products
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Conversion of the numerous aryl ketones into aryl electrophiles via Ar-C(O) cleavage remains a challenging yet highly desirable transformation in Sonogashira-type coupling. Herein, we report a palladium-catalyzed ligand-promoted alkynylation of unstrained aryl ketones. The protocol allows the alkynylation to be carried out in a one-pot procedure with broad functional-group tolerance and substrate scope. The potential applications of this protocol in drug discovery and chemical biology are further demonstrated by late-stage diversification of a number of pharmaceuticals and natural products. More importantly, two different biologically important fragments derived from a pharmaceutical and natural product could be connected by the consecutive alkynylation of ketones. Distinct from aryl halides in conventional Sonogashira reactions, the protocol provides a practical tool for the 1,2-bifunctionalization of aryl ketone by merging ketone-directed ortho-C-H activation with ligand-promoted ipso-Ar-C(O) alkynylation.
- Xu, Hui,Ma, Biao,Fu, Zunyun,Li, Han-Yuan,Wang, Xing,Wang, Zhen-Yu,Li, Ling-Jun,Cheng, Tai-Jin,Zheng, Mingyue,Dai, Hui-Xiong
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p. 1758 - 1764
(2021/02/09)
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- Simple and efficient diaryl alkyne synthesis method
-
The embodiment of the invention discloses a simple and efficient diaryl alkyne synthesis method. The method comprises the steps of by taking arylmethylbenzotriazole and aromatic aldehyde as raw materials, carrying out addition and double-beta-elimination reaction under the action of bis (trimethylsilyl) amino salt MN (SiMe3) 2 to synthesize diaryl alkyne by a one-pot method. The raw materials and chemical reagents used in the method are easy to obtain, the reaction conditions are mild, the operation is simple, the substrate universality is good, the product yield is high, and the method is a simple and efficient diaryl alkyne synthesis method.
- -
-
Paragraph 0026; 0029-0031
(2021/04/14)
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- Encapsulating palladium nanoparticles inside ethylenediamine functionalized and crosslinked chlorinated poly(vinyl chloride) nanofibers as an efficient and stable heterogeneous catalyst for coupling reactions
-
Palladium chloride and chlorinated poly (vinyl chloride) (CPVC) mixture were prepared into homogeneous solution, followed by electrospinning to make uniform nanofibers with average diameter of ~460 nm. Then, these composite nanofibers were treated in ethy
- Du, Yijun,Qi, Chenze,Qin, Min,Shao, Linjun,Tao, Hongyu,Wang, Qingqing
-
-
- Incorporation of Palladium Catalyst Inside Cross-Linked Chitosan Hybrid Nanofibers for the Sonogashira Reaction
-
Abstract: Nanofibers are attractive supporting matrices for catalytically active metallic catalysts. Herein, palladium species were successfully incorporated into the modified chitosan/poly(ethylene oxide)/maleic acid nanofibers by electrospinning. Then,
- Zhong, S.
-
p. 480 - 485
(2020/07/03)
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- Trithiocarbonate Anion as a Sulfur Source for the Synthesis of 2,5-Disubstituted Thiophenes and 2-Substituted Benzo[ b]thiophenes
-
The trithiocarbonate anion (CS32-) was generated in situ from CS2 and KOH in dimethyl sulfoxide by a simple method and used as a novel synthetic equivalent of the S2- synthon for the synthesis of 2,5-disubstituted thiophenes from 1,3-butadiynes. Additionally, this system was employed for the metal-free synthesis of 2-substituted benzo[b]thiophenes from 2-haloalkynyl (hetero)arenes. These compounds were obtained from a cheap and readily available sulfur source in moderate to good yields, with good functional group tolerance.
- Paix?o, Douglas B.,Rampon, Daniel S.,Salles, Helena D.,Soares, Eduardo G. O.,Bilheri, Filipe N.,Schneider, Paulo H.
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supporting information
p. 12922 - 12934
(2020/11/26)
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- Gold-Catalyzed Hydrofluorination of Internal Alkynes Using Aqueous HF
-
The gold-catalyzed hydrofluorination reaction of internal alkynes using hydrofluoric acid is reported. Notably, those conditions use one of the most economical sources of HF and are free of additional additives. Both symmetrical and unsymmetrical internal alkynes can be utilized, and the use of alkynes bearing a fluorinated group at the propargylic position as substrates allowed for a regioselective hydrofluorination reaction.
- Gauthier, Rapha?l,Mamone, Marius,Paquin, Jean-Fran?ois
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supporting information
p. 9024 - 9027
(2019/11/14)
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- Arylation of Terminal Alkynes by Aryl Iodides Catalyzed by a Parts-per-Million Loading of Palladium Acetate
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Arylation of terminal alkynes (16 varieties) by aryl iodides (28 varieties) was achieved with a mol ppm loading level of palladium catalyst, where a variety of functional groups including heteroarenes were tolerated. Thus, the arylations were carried out in the presence of palladium acetate at ppm loadings and potassium carbonate in ethanol at 80 °C to give the corresponding internal alkynes in good to excellent yields. Synthesis of 2-phenyl-3-(phenylalkynyl)benzofuran was achieved by iterative use of the alkyne arylation under mol ppm catalytic conditions. Reaction-rate analysis, transmission electron microscopic (TEM) examination of the reaction mixture, and mercury-amalgamation test were performed to gain insight into the active species of the highly active ppm catalytic species. TEM examination of the reaction mixture revealed that palladium nanoparticles were generated in situ under the reaction conditions, and their cluster size was variable during the catalytic reaction. A variation in size of palladium particles suggested that the composition-decomposition process of Pd aggregates should take place in situ via monomeric palladium(0) species and/or fine palladium(0) clusters, which might be real catalytic species in this reaction.
- Hamasaka, Go,Roy, David,Tazawa, Aya,Uozumi, Yasuhiro
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p. 11640 - 11646
(2019/12/02)
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- Highly efficient synthesis of 1,2-disubstituted acetylenes derivatives from the cross-coupling reactions of 1-bromoalkynes with organoalane reagents
-
A Highly efficient route for the synthesis of 1,2-disubstituted acetylene derivatives has been developed by palladium catalyzed cross-couplings of alkynyl halides with (hetero)aryl aluminium reagents under mild conditions. This has given corresponding cross-coupling products good to excellent isolated yields of up to 99%. The aryls bearing electron-donating or electron-withdrawing groups in either alkynylhalides or arylaluminum substrates gave cross-coupling products good yields. This process was simple and easily performed, which provides an efficient method for the synthesis of 1,2-disubstituted acetylenes derivatives. On the basis of the experimental results, a possible catalytic cycle has been proposed.
- Shao, Xue-Bei,Jiang, Xin,Li, Qing-Han,Zhao, Zhi-Gang
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p. 6063 - 6070
(2018/09/12)
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- Ligand- and copper-free Sonogashira and Heck couplings of (Het)aryl chlorides and bromides catalyzed by palladium nanoparticles supported on in situ generated Al(OH)3
-
The ligand- and copper-free Sonogashira reaction of (Het)aryl halides (Br and Cl) with various terminal alkynes and the Heck coupling of (Het)aryl halides (Br and Cl) with a series of olefins, catalyzed by palladium nanoparticles supported on newly generated Al(OH)3, were developed. The catalyst can be readily recovered and reused 6 times without significant loss of activity and palladium leaching.
- Li, Xing,Gong, Xiaolei,Li, Zhipeng,Chang, Honghong,Gao, Wenchao,Wei, Wenlong
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p. 2475 - 2479
(2017/02/05)
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- Further insight into the photochemical behavior of 3-aryl-N-(arylsulfonyl)propiolamides: tunable synthetic route to phenanthrenes
-
Reported herein is further insight into the photochemical behaviour of 3-aryl-N-(arylsulfonyl)-propiolamides, which provides a straightforward way to access meaningful phenanthrenes. Mechanistic investigation indicated that aryl migration, C-C coupling, 1,3-hydrogen shift, desulfonylation and elimination were involved in the process. Moreover, this protocol allowed for scale-up using a flow reactor.
- Chen, Ming,Zhao, Xinxin,Yang, Chao,Wang, Yanpei,Xia, Wujiong
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p. 12022 - 12026
(2017/03/01)
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- Method for synthesizing multi-substituted alkyne
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The invention discloses a method for synthesizing multi-substituted alkyne, relates to the technical field of synthesis of multi-substituted alkyne and provides a method for synthesizing multi-substituted alkyne through terminal alkyne and halide of sp2 type carbon under the catalysis of a polyaniline supported nano-palladium catalyst. According to the method, polyaniline supported nano-palladium is taken as a catalyst, diisopropyl-2-ethyoxyl ethylamine is taken as alkali, and multi-substituted alkyne is directly synthesized in one step through cross coupling. Compared with conventional methods, the method has the advantages that raw materials are simple and easy to obtain, the cost is low, the catalyst is mild, environment-friendly and rich, and a solvent is clean and environment-friendly. Thus, a clean and practical synthesis method is provided for synthesis of such important compounds.
- -
-
Paragraph 0012; 0013; 0022; 0023
(2016/11/24)
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- Gram-Scale Preparation of Pd@PANI: A Practical Catalyst Reagent for Copper-Free and Ligand-Free Sonogashira Couplings
-
Palladium nanoparticles on the polyaniline (Pd@PANI) catalyst are now easily prepared on a gram scale through the oxidative polymerization of aniline in the presence of PdCl2 by using air as a clean oxidant. The material is found to be very stable and can be stored for more than one year without deactivation. Thus, it may become a commercial reagent in organic synthesis, depending on its application scopes. This article reported the first example of Pd@PANI-catalyzed Sonogashira couplings free of copper and ligands.
- Yu, Lei,Han, Zhe,Ding, Yuanhua
-
p. 2124 - 2129
(2016/12/24)
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- Visible light-mediated gold-catalysed carbon(sp2)-carbon(sp) cross-coupling
-
A dual photoredox and gold-catalysed cross-coupling reaction of alkynyltrimethylsilanes and aryldiazonium tetrafluoroborates is described. The reaction proceeds through visible-light mediated oxidative addition of aryldiazoniums, transmetalation of alkynyltrimethylsilanes and aryl-alkynyl reductive elimination. Exclusive selectivity for silyl-substituted alkynes is observed, with no reactivity observed for terminal alkynes.
- Kim, Suhong,Rojas-Martin, Jaime,Toste, F. Dean
-
-
- Organocatalytic synthesis of alkynes
-
Carbon-carbon triple bonds of alkynes are ubiquitous. They serve as valuable starting materials that can be transformed into a vast array of diverse materials, with applications ranging from medicinal chemistry to electronic materials. The methods used to prepare alkynes involve stoichiometric reactions and the most popular install only a single carbon rather than uniting larger fragments. These methods are useful, but they are limited by harsh conditions or the need to prepare reagents. Introduced herein is the first catalytic method to prepare carbon-carbon triple bonds from precursors that do not contain such linkages. By coupling benzaldehyde and benzyl chloride derivatives under basic conditions with an organocatalyst, good yields of alkynes are obtained. The catalyst, a highly reactive sulfenate anion, is readily generated under the reaction conditions from air-stable precursors. This method represents an attractive organocatalytic alternative to well-established stoichiometric approaches to alkynes and to transition-metal-based alkyne functionalization methods in various applications.
- Zhang, Mengnan,Jia, Tiezheng,Wang, Carol Y.,Walsh, Patrick J.
-
supporting information
p. 10346 - 10350
(2015/09/01)
-
- Stereoselective iron-catalyzed alkyne hydrogenation in ionic liquids
-
Iron(0) nanoparticles in ionic liquids (ILs) have been shown to catalyse the semi-hydrogenation of alkynes. In the presence of a nitrile-functionalised IL or acetonitrile, stereoselective formation of (Z)-alkenes was observed. The biphasic solvent system allowed facile separation and re-use of the catalyst. The Royal Society of Chemistry 2014.
- Gieshoff, Tim N.,Welther, Alice,Kessler, Michael T.,Prechtl, Martin H.G.,Jacobi Von Wangelin, Axel
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supporting information
p. 2261 - 2264
(2014/03/21)
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- An alternative role for acetylenes: Activation of fluorobenzenes toward nucleophilic aromatic substitution
-
Acetylenes are increasingly versatile functional groups for a range of complexity-building organic transformations and for the construction of desirable molecular architectures. Herein we disclose a previously underappreciated aspect of arylacetylene reac
- Bizier, Nicholas P.,Wackerly, Jay Wm.,Braunstein, Eric D.,Zhang, Mengfei,Nodder, Stephen T.,Carlin, Stephen M.,Katz, Jeffrey L.
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p. 5987 - 5998
(2013/07/26)
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- Gold and palladium combined for the Sonogashira coupling of aryl and heteroaryl halides
-
A highly efficient gold and palladium combined methodology for the Sonogashira coupling of a wide array of electronically and structurally diverse aryl and heteroaryl halides is described. The orthogonal reactivity of the two metals shows high selectivity and extreme functional group tolerance in Sonogashira coupling. A brief mechanistic study reveals that the gold acetylide intermediate enters into the palladium catalytic cycle at the transmetalation step. Georg Thieme Verlag Stuttgart.New York.
- Panda, Biswajit,Sarkar, Tarunk.
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p. 817 - 829
(2013/04/10)
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- Sonogashira/hydroarylation sequential reactions: Catalyzed by NHC-Pd complexes
-
It was found that an air-stable NHC-palladium complex of Pd[(s)-3-C 3H5-4-(C5H5CH2)-1-(2,6- iPr2C6H3)-C3H 3N2](C5H5N)Br2 derived from l-phenylalanine is an effective pre-catalyst for copper-free and phosphine-free Sonogashira reaction of alkynes under aerobic conditions in short reaction time. Moreover, the palladium compound would be reused to catalyze the hydroarylation of alkyne prepared from Sonogashira reaction, which makes firstly Sonogashira/Hydroarylation sequential reactions successful. The arylation of alkynes underwent with a high regio- and stereoselectivity and only trans-arylation of alkyne was observed. No Z/E isomerization of the olefin was observed in the system.
- Yang, Longguang,Li, Yunfei,Chen, Qian,Du, Yufeng,Cao, Changsheng,Shi, Yanhui,Pang, Guangsheng
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p. 5178 - 5184
(2013/06/27)
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- Synthesis and characterization of novel chiral NHC-palladium complexes and their application in copper-free Sonogashira reactions
-
A new series of chiral N-heterocyclic carbene (NHC) palladium complexes were synthesized from a relatively inexpensive amino acid, l-phenylalanine. All these compounds were fully characterized by 1H-NMR, 13C-NMR and elemental analysis. The X-ray molecular structures of two of the complexes were reported. The catalytic activity of the four palladium complexes was successfully tested in the Sonogashira reaction under copper free conditions in air. The palladium complex 3a provided good activity in the Sonogashira coupling reaction. The Royal Society of Chemistry 2012.
- Yang, Longguang,Guan, Pei,He, Pan,Chen, Qian,Cao, Changsheng,Peng, Yu,Shi, Zhan,Pang, Guangsheng,Shi, Yanhui
-
experimental part
p. 5020 - 5025
(2012/06/04)
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- Highly selective iron-catalyzed synthesis of alkenes by the reduction of alkynes
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Herein, the iron-catalyzed reduction of a variety of alkynes with silanes as a reductant has been examined. With a straightforward catalyst system composed of diiron nonacarbonyl and tributyl phosphane, excellent yields and chemoselectivities (>99 %) were obtained for the formation of the corresponding alkenes. After studying the reaction conditions, and the scope and limitations of the reaction, several attempts were undertaken to shed light on the reaction mechanism. Im Rahmen dieser Arbeit wird die Eisen-katalysierte Reduktion von Alkinen zu den entsprechenden Alkenen mit Hilfe von Silanen vorgestellt. Hierbei konnten exzellente Ausbeuten und Selektivitaeten (>99 %) durch die Modifikation des eingesetzten Eisenkatalysators mit Phosphanen beobachtet werden. Nach genauer Untersuchung verschiedenster Reaktionsparameter wurden die hervorragenden Eigenschaften des Katalysatorsystems in der Reduktion zahlreicher Alkine gezeigt. Zum besseren Verstaendnis der Reaktion wurden verschiedene mechanistische Experimente durchgefuehrt. Iron Made′m: In situ generated iron complexes catalyze the reduction of alkynes with silanes as a hydride source with excellent selectivity (>99 %). Copyright
- Enthaler, Stephan,Haberberger, Michael,Irran, Elisabeth
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experimental part
p. 1613 - 1623
(2012/06/04)
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- An Efficient and Recyclable Mesostructured Polymer-Supported N-Heterocyclic Carbene-Palladium Catalyst for Sonogashira Reactions
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Palladium catalyst systems are the most widely used for the formation of C-C and C-N bonds. Environmentally friendly heterogeneous palladium catalysts have strongly stimulated growth in this research area. Herein, a FDU (Fudan University)-15 mesopolymer w
- Yu, Tao,Li, Ying,Yao, Chengfu,Wu, Haihong,Liu, Yueming,Wu, Peng
-
p. 1712 - 1718
(2016/04/10)
-
- Gold-catalyzed synthesis of benzil derivatives and α-keto imides via oxidation of alkynes
-
An efficient process based on the gold-catalyzed redox reaction has been developed to oxidize 1,2-diarylacetylene or ynamide to 1,2-diaryldiketone or α-keto imide respectively. This process can tolerate a variety of functional groups and affords 1,2-dicarbonyl compounds in excellent yields under mild reaction conditions.
- Xu, Cheng-Fu,Xu, Mei,Jia, Yi-Xia,Li, Chuan-Ying
-
supporting information; experimental part
p. 1556 - 1559
(2011/04/26)
-
- On the catalytic duo PdCl2(PPh3)2/AuCl(PPh3) that cannot effect a Sonogashira-type reaction: a correction
-
In contrast to the observation made by the Laguna group, we report that the combination of PdCl2(PPh3)2 and AuCl(PPh3) makes a unique catalytic system that allows Sonogashira-type cross-coupling of both aryl and alkyl alkynes with aryl halides in excellent yields.
- Panda, Biswajit,Sarkar, Tarun K.
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experimental part
p. 301 - 305
(2010/03/26)
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- The first Cu- and amine-free Sonogashira-type cross-coupling in the C-6-alkynylation of protected 2′-deoxyadenosine
-
The Sonogashira cross-coupling reaction offers a convenient route to C(sp)-C(sp2) bond formation. Although the Sonogashira reaction has traditionally been carried out in the presence of Pd catalyst and a co-catalyst of Cu(I) salt, the use of Cu(I) salt is often not efficient because it leads to the formation of unwanted side-products. This has prompted interest in recent years in the development of Cu-free Sonogashira cross-coupling reaction conditions. In addition, the development of Cu-free Sonogashira cross-coupling conditions for the alkynylation of nucleoside derivatives remains largely unexplored. Herein, we demonstrate that Cu- and amine-free Sonogashira-type cross-coupling lead to successful alkynylation of aryl bromides and heteroaryl bromides. For the first time, we have extended this method for the alkynylation of protected 2′-deoxyadenosine at the C-6 position.
- Ngassa, Felix N.,Lindsey, Erick A.,Haines, Brandon E.
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supporting information; experimental part
p. 4085 - 4091
(2009/09/30)
-
- Ethynyl-cyclohexanol: an efficient acetylene surrogate in Sonogashira coupling
-
The Sonogashira coupling of aryl halides in the presence of 1-ethynyl-cyclohexanol as an acetylene source provides an efficient method for the synthesis of diarylacetylenes without the isolation of the appropriate arylacetylenes.
- Csékei, Márton,Novák, Zoltán,Kotschy, András
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p. 975 - 982
(2008/09/17)
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- Copper-free Sonogashira coupling in amine-water solvent mixtures
-
Extensive study of different amine-water solvent mixtures was carried out for copper free Sonogashira coupling of aryl iodides. The influence of the palladium sources, ligands, amine-water ratio and further additives was also evaluated. Application of sec-butylamine-water mixture proved to be an excellent medium for rapid and efficient coupling of aryl-iodides at ambient temperature in the presence of PdCl2(PPh3)2 as catalyst.
- Komáromi, Anna,Tolnai, Gergely László,Novák, Zoltán
-
supporting information; experimental part
p. 7294 - 7298
(2009/04/11)
-
- Gold(I) iodide catalyzed sonogashira reactions
-
Gold(I) iodide catalyzed Sonogashira reactions have been developed. Terminal alkynes reacted with aryl iodides and bromides smoothly in the presence of AuI (1 mol-%) and dppf (1 mol-%) in toluene to generate the corresponding cross-coupling products in good to excellent yields. Furthermore, aromatic terminal alkynes could also react with 2-iodoaniline to form substituted indoles in excellent yields through a coupling-cyclization reaction sequence under the present reaction conditions. Wiley-VCH Verlag GmbH & Co. KGaA, 2009.
- Li, Pinhua,Wang, Lei,Wang, Min,You, Feng
-
scheme or table
p. 5946 - 5951
(2009/05/27)
-
- Can polarization of triple bond in tolanes be deduced from 13C NMR shifts? Re-evaluation of factors affecting regiochemistry of the palladium-catalyzed hydrostannation of alkynes
-
Polarization of the triple bond in a series of differently substituted ortho and para-tolanes has been studied by NMR and computational methods in order to examine if 13C NMR data can be effectively used for the assessment of electronic polarization of a triple bond in diarylacetylenes. DFT calculations of both natural charges and NMR properties revealed that chemical shifts concur with effective charges on sp-carbon atoms in para-tolanes, whereas in ortho-analogues magnetic anisotropy complicates the analysis making 13C NMR data inapplicable for ascribing triple bond polarization. The obtained information was used to reevaluate factors affecting the regiochemistry of the Pd-catalyzed hydrostannation of the triple bond in tolanes. Computational study on the polarization of triple bonds taken together with the experimental data on hydrostannation of various mono- and disubstituted tolanes bearing para- and ortho-substituents demonstrated that the regioselectivity of hydrostannation is governed by a combination of electronic and steric factors. In para-tolanes, the electronic effect prevails and α- and β-vinylstannanes are obtained predominantly for substrates with electron-withdrawing and electron-donating groups, respectively. In the ortho-series, steric factors dominate over electronics and α-isomers are produced with high selectivity regardless of the substituents' nature. However, it was found that in disubstituted "push-pull" tolanes steric control of an ortho-group can be overruled by the very strong electronic effect of an electron-withdrawing substituent in para-position.
- Rubin, Michael,Trofimov, Alexander,Gevorgyan, Vladimir
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p. 10243 - 10249
(2007/10/03)
-
- Aryl alkynylation versus alkyne homocoupling: Unprecedented selectivity switch in Cu, phosphine and solvent-free heterogeneous Pd-catalysed couplings
-
Sonogashira reaction and oxidative dimerisation of terminal alkynes are among the most relevant and attractive C-C bond forming transformations in the metallo-catalysed cross-coupling scenario. Often, the homocoupling reactions of substituted acetylenic derivatives are concomitant to the Sonogashira pathway and time-consuming optimization procedures are required in order to reach satisfactory levels of selectivity. In this paper, the potential of a class of Pd-complexes loaded to mesoporous silica gel in promoting the Sonogashira reaction between aryl acetylenes and iodoarenes is underlined. This family of heterogeneous organo-palladium systems allows the desired cross-coupled compounds to be isolated in excellent yield under very mild conditions. In fact, the absence of organic solvents, copper(I) co-catalyst and phosphane ligands, (which are easily oxidisable and whose preparation has a heavy environmental impact), in conjunction with the low catalyst loading ([Pd] 0.1-1 mol%) and its recoverability, stresses the environmental benefits of the protocol. The Sonogashira/homocoupling selectivity proved to be function of the haloarene employed. As a matter of fact, while iodoarenes bearing EWG (electron withdrawing groups) on the phenyl ring underwent smoothly the Sonogashira pathway, electron-rich iodobenzenes showed opposite behaviour by mainly furnishing the homocoupling product. The use of bromoarenes provided solely the homocoupling product in excellent yield without themselves being consumed. This is despite that fact that the catalysts used activate bromoarenes equally as well as iodoarenes in both Heck and Suzuki systems. Kinetic investigations revealed a highly temperature-dependent profile, which indicates strongly that the reaction takes place at the surface. Finally, the full heterogeneous character of the catalytically active species as well as the reusability of the immobilised Pd-complex were confirmed by hot-filtration test and by multiple reuses of the supported catalyst in subsequent Sonogashira cross-couplings.
- Bandini, Marco,Luque, Rafael,Budarin, Vitaly,Macquarrie, Duncan J.
-
p. 9860 - 9868
(2007/10/03)
-
- Palladium-tetraphosphine complex: An efficient catalyst for the alkynylation of ortho-substituted aryl bromides
-
The tetraphosphine cis,cis,cis-1,2,3,4-tetrakis(diphenylphosphinomethyl) cyclopentane in combination with [Pd(C3H5)Cl]2 affords a very efficient catalyst for the alkynylation of ortho-substituted aryl bromides. A wide variety of substituents such as phenyl, trifluoromethyl, acetyl, formyl or nitrile, are tolerated. High turnover numbers can be obtained with most of these aryl bromides. The coupling of sterically very congested aryl bromides such as 9-bromoanthracene or 2,4,6-triisopropylbromobenzene also proceeds in good yields.
- Feuerstein, Marie,Berthiol, Florian,Doucet, Henri,Santelli, Maurice
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p. 1281 - 1289
(2007/10/03)
-
- Sonogashira coupling and cyclization reactions on alumina: A route to aryl alkynes, 2-substituted-benzo[b]furans and 2-substituted-indoles
-
A solventless, microwave-enhanced Sonogashira coupling reaction of aromatic iodides with terminal alkynes on potassium fluoride doped alumina in the presence of palladium powder, cuprous iodide, and triphenylphosphine has been developed. The reaction can be utilized to prepare aryl alkynes in excellent yields. The coupling of o-iodophenol with terminal alkynes leads to the formation 2-substituted-benzo[b]furans. Whereas the coupling of o-iodoanilines with terminal alkynes generates indole products. An in situ desilylation reaction was also developed.
- Kabalka, George W.,Wang, Lei,Pagni, Richard M.
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p. 8017 - 8028
(2007/10/03)
-