1
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Stevens JE, Miller JD, Fitzsimmons MC, Moore CE, Thomas CM. Z-selective dimerization of terminal alkynes by a (PNNP)Fe II complex. Chem Commun (Camb) 2024; 60:5169-5172. [PMID: 38639737 DOI: 10.1039/d4cc00469h] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 04/20/2024]
Abstract
A tetradentate bis(amido)bis(phosphine) FeII complex, (PNNP)Fe, is shown to activate the terminal C-H bond of aryl alkynes across its Fe-Namide bonds. (PNNP)Fe is also shown to catalytically dimerize terminal aryl alkynes to produce 1,3-enynes with Z : E ratios as high as 96 : 4 with yields up to 95% and loadings as low as 1 mol% at 30 °C in 2 h. A plausible metal-ligand cooperative mechanism invoking a vinylidene intermediate is proposed.
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Affiliation(s)
- Jeremiah E Stevens
- Department of Chemistry and Biochemistry, The Ohio State University, 100 W. 18th Ave., Columbus, OH 43210, USA.
| | - Justin D Miller
- Department of Chemistry and Biochemistry, The Ohio State University, 100 W. 18th Ave., Columbus, OH 43210, USA.
| | - Matthew C Fitzsimmons
- Department of Chemistry and Biochemistry, The Ohio State University, 100 W. 18th Ave., Columbus, OH 43210, USA.
| | - Curtis E Moore
- Department of Chemistry and Biochemistry, The Ohio State University, 100 W. 18th Ave., Columbus, OH 43210, USA.
| | - Christine M Thomas
- Department of Chemistry and Biochemistry, The Ohio State University, 100 W. 18th Ave., Columbus, OH 43210, USA.
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2
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Chen H, Yang W, Zhang J, Lu B, Wang X. Divergent Geminal Alkynylation-Allylation and Acylation-Allylation of Carbenes: Evolution and Roles of Two Transition-Metal Catalysts. J Am Chem Soc 2024; 146:4727-4740. [PMID: 38330247 DOI: 10.1021/jacs.3c12162] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/10/2024]
Abstract
Cooperative bimetallic catalysis to access novel reactivities is a powerful strategy for reaction development in transition-metal-catalyzed chemistry. Particularly, elucidation of the evolution of two transition-metal catalysts and understanding their roles in dual catalysis are among the most fundamental goals for bimetallic catalysis. Herein, a novel three-component reaction of a terminal alkyne, a diazo ester, and an allylic carbonate was successfully developed via cooperative Cu/Rh catalysis with Xantphos as the ligand, providing a highly efficient strategy to access 1,5-enynes with an all-carbon quaternary center that can be used as immediate synthetic precursors for complex cyclic molecules. Notably, a Meyer-Schuster rearrangement was involved in the reactions using propargylic alcohols, resulting in an unprecedented acylation-allylation of carbenes. Mechanistic studies suggested that in the course of the reaction Cu(I) species might aggregate to some types of Cu clusters and nanoparticles (NPs), while the Rh(II)2 precursor can dissociate to mono-Rh species, wherein Cu NPs are proposed to be responsible for the alkynylation of carbenes and work in cooperation with Xantphos-coordinated dirhodium(II) or Rh(I)-catalyzed allylic alkylation.
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Affiliation(s)
- Hongda Chen
- State Key Laboratory of Organometallic Chemistry, Center for Excellence in Molecular Synthesis, Shanghai Institute of Organic Chemistry, University of Chinese Academy of Sciences, Chinese Academy of Sciences, 345 Lingling Road, Shanghai 200032, China
| | - Wenhan Yang
- State Key Laboratory of Organometallic Chemistry, Center for Excellence in Molecular Synthesis, Shanghai Institute of Organic Chemistry, University of Chinese Academy of Sciences, Chinese Academy of Sciences, 345 Lingling Road, Shanghai 200032, China
| | - Jinyu Zhang
- State Key Laboratory of Organometallic Chemistry, Center for Excellence in Molecular Synthesis, Shanghai Institute of Organic Chemistry, University of Chinese Academy of Sciences, Chinese Academy of Sciences, 345 Lingling Road, Shanghai 200032, China
| | - Bin Lu
- State Key Laboratory of Organometallic Chemistry, Center for Excellence in Molecular Synthesis, Shanghai Institute of Organic Chemistry, University of Chinese Academy of Sciences, Chinese Academy of Sciences, 345 Lingling Road, Shanghai 200032, China
| | - Xiaoming Wang
- State Key Laboratory of Organometallic Chemistry, Center for Excellence in Molecular Synthesis, Shanghai Institute of Organic Chemistry, University of Chinese Academy of Sciences, Chinese Academy of Sciences, 345 Lingling Road, Shanghai 200032, China
- School of Chemistry and Materials Science, Hangzhou Institute for Advanced Study, University of Chinese Academy of Sciences, 1 Sub-Lane Xiangshan, Hangzhou 310024, China
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3
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Sun Y, Zhang J, Zeng Y, Meng L, Li X. Mechanism and Stereoselectivity Control of Terminal Alkyne Dimerization Activated by a Zr/Co Heterobimetallic Complex: A DFT Study. J Org Chem 2024; 89:605-616. [PMID: 38096545 DOI: 10.1021/acs.joc.3c02359] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2024]
Abstract
Heterobimetallic complexes have recently garnered considerable attention in organic synthesis owing to their high activity and selectivity, which surpass those of monometallic complexes. In this study, the detailed mechanisms of terminal alkyne dimerization activated by the heterobimetallic Zr/Co complex, as well as the different stereoselectivities of Me3SiC≡CH and PhC≡CH dimerization, were investigated and elucidated by using density functional theory calculations. After excluding the three-molecule reaction and outer-sphere mechanisms, the inner-sphere mechanism was determined as the most optimal process. The inner-sphere mechanism involves four processes: THF dissociation and coordination of the first alkyne; ligand migration and C-H activation; N2 dissociation and insertion of the second alkyne; and reductive elimination. The stereoselectivity between the E-/Z- and gem-isomers is determined by the C-C coupling mode of the two alkynes and that of the E- and Z-isomers is determined by the sequence of the C-C coupling and hydrogen migration in the reductive elimination process. Me3SiC≡CH dimerization yields only an E-isomer owing to the large differences in the distortion and interaction energies, whereas PhC≡CH dimerization produces an E-, Z-, and gem-isomers owing to the reduced interaction energy differences.
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Affiliation(s)
- Yuanyuan Sun
- College of Chemistry and Material Science, Hebei Key Laboratory of Inorganic and Nano-Materials, National Demonstratin Center for Experimental Chemistry, Hebei Normal University, Shijiazhuang 050024, P. R. China
| | - Jinying Zhang
- College of Chemistry and Material Science, Hebei Key Laboratory of Inorganic and Nano-Materials, National Demonstratin Center for Experimental Chemistry, Hebei Normal University, Shijiazhuang 050024, P. R. China
| | - Yanli Zeng
- College of Chemistry and Material Science, Hebei Key Laboratory of Inorganic and Nano-Materials, National Demonstratin Center for Experimental Chemistry, Hebei Normal University, Shijiazhuang 050024, P. R. China
| | - Lingpeng Meng
- College of Chemistry and Material Science, Hebei Key Laboratory of Inorganic and Nano-Materials, National Demonstratin Center for Experimental Chemistry, Hebei Normal University, Shijiazhuang 050024, P. R. China
| | - Xiaoyan Li
- College of Chemistry and Material Science, Hebei Key Laboratory of Inorganic and Nano-Materials, National Demonstratin Center for Experimental Chemistry, Hebei Normal University, Shijiazhuang 050024, P. R. China
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4
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Duchemin C, Kim J, Chirik PJ. CS-Symmetric Pyridine(diimine) Iron Methyl Complexes for Catalytic [2+2] Cycloaddition and Hydrovinylation: Metallacycle Geometry Determines Selectivity. JACS AU 2023; 3:2007-2024. [PMID: 37502155 PMCID: PMC10369671 DOI: 10.1021/jacsau.3c00229] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 05/06/2023] [Revised: 06/17/2023] [Accepted: 06/20/2023] [Indexed: 07/29/2023]
Abstract
A series of CS-symmetric (aryl,alkyl)-substituted pyridine(dimine) iron methyl (CyARPDI)FeCH3 complexes have been prepared, characterized, and evaluated as precatalysts for the [2+2]-cycloaddition of butadiene and ethylene. Mixtures of vinylcyclobutane and (Z)-hexa-1,4-diene were observed in each case. By comparison, C2v-symmetric, arylated (PDI) iron catalysts are exclusively selective for reversible [2+2]-cycloaddition to yield vinylcyclobutane. The alteration in the chemoselectivity of the catalytic reaction was investigated through a combination of precatalyst stability studies, identification of catalytic resting state(s), and 2H and 13C isotopic labeling experiments. While replacement of an aryl-imine substituent with an N-alkyl group decreases the stability of the formally iron(0) dinitrogen and butadiene complexes, two diamagnetic metallacycles were identified as catalyst resting states. Deuterium labeling and NOESY/EXSY NMR experiments support 1,4-hexadiene arising from catalytic hydrovinylation involving reversible oxidative cyclization leading to accessible cis-metallacycle. Cyclobutane formation proceeds by irreversible C(sp3)-C(sp3) bond-forming reductive elimination from a trans-metallacycle. These studies provide key mechanistic understanding into the high selectivity of bis(arylated) pyridine(diimine) iron catalysts for [2+2]-cycloaddition, unique, thus far, to this class of iron catalysts.
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5
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Wang Z, Zhang C, Wu J, Li B, Chrostowska A, Karamanis P, Liu SY. trans-Hydroalkynylation of Internal 1,3-Enynes Enabled by Cooperative Catalysis. J Am Chem Soc 2023; 145:5624-5630. [PMID: 36862947 PMCID: PMC10162690 DOI: 10.1021/jacs.3c00514] [Citation(s) in RCA: 7] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 03/04/2023]
Abstract
A cooperative catalyst system involving a Pd(0)/Senphos complex, tris(pentafluorophenyl)borane, copper bromide, and an amine base, is demonstrated to catalyze trans-hydroalkynylation of internal 1,3-enynes. For the first time, a Lewis acid catalyst is shown to promote the reaction involving the emerging outer-sphere oxidative reaction step. The resulting cross-conjugated dieneynes are versatile synthons for organic synthesis, and their characterization reveals distinct photophysical properties depending on the positioning of the donor/acceptor substituents along the conjugation path.
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Affiliation(s)
- Ziyong Wang
- Department of Chemistry, Boston College, Chestnut Hill, Massachusetts 02467-3860, United States
| | - Chen Zhang
- Université de Pau et des Pays de l'Adour, E2S UPPA/CNRS, Institut des Sciences Analytiques et de Physico-Chimie pour l'Environnement et les Matériaux IPREM UMR 5254. Hélioparc, 2 Avenue P. Angot, 64053 Pau Cedex 09, France
| | - Jason Wu
- Department of Chemistry, Boston College, Chestnut Hill, Massachusetts 02467-3860, United States
| | - Bo Li
- Department of Chemistry, Boston College, Chestnut Hill, Massachusetts 02467-3860, United States
| | - Anna Chrostowska
- Université de Pau et des Pays de l'Adour, E2S UPPA/CNRS, Institut des Sciences Analytiques et de Physico-Chimie pour l'Environnement et les Matériaux IPREM UMR 5254. Hélioparc, 2 Avenue P. Angot, 64053 Pau Cedex 09, France
| | - Panaghiotis Karamanis
- Université de Pau et des Pays de l'Adour, E2S UPPA/CNRS, Institut des Sciences Analytiques et de Physico-Chimie pour l'Environnement et les Matériaux IPREM UMR 5254. Hélioparc, 2 Avenue P. Angot, 64053 Pau Cedex 09, France
| | - Shih-Yuan Liu
- Department of Chemistry, Boston College, Chestnut Hill, Massachusetts 02467-3860, United States
- Université de Pau et des Pays de l'Adour, E2S UPPA/CNRS, Institut des Sciences Analytiques et de Physico-Chimie pour l'Environnement et les Matériaux IPREM UMR 5254. Hélioparc, 2 Avenue P. Angot, 64053 Pau Cedex 09, France
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6
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Luo A, Zhou H, Zhou Q, Hua Q, Zhao X, Yu X, Yang K, Hu YJ. On-DNA Alkyne Iodination and Acetylenic Coupling as a Useful Tool for DEL Synthesis. Bioconjug Chem 2022; 33:2299-2306. [PMID: 36450158 DOI: 10.1021/acs.bioconjchem.2c00471] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/05/2022]
Abstract
1-Iodoalkynes and 1,3-diynes are versatile chemical intermediates and pharmaceutically valuable ingredients. In this study, copper mediated on-DNA alkyne iodination and Cadiot-Chodkiewicz coupling are developed for the first time. This generates diverse, systematic, and unprecedented topographic structural features, which could be invaluable as molecular recognition agents for drug discovery in DEL screening.
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Affiliation(s)
- Ayun Luo
- Pharmaron (Ningbo) Technology Development Co., Ltd. No. 800 Bin-Hai 4th Road, Hangzhou Bay New Zone, Ningbo, 315336, China
| | - Hongxia Zhou
- Pharmaron (Ningbo) Technology Development Co., Ltd. No. 800 Bin-Hai 4th Road, Hangzhou Bay New Zone, Ningbo, 315336, China
| | - Qi Zhou
- Pharmaron (Ningbo) Technology Development Co., Ltd. No. 800 Bin-Hai 4th Road, Hangzhou Bay New Zone, Ningbo, 315336, China
| | - Qini Hua
- Pharmaron (Ningbo) Technology Development Co., Ltd. No. 800 Bin-Hai 4th Road, Hangzhou Bay New Zone, Ningbo, 315336, China
| | - Xue Zhao
- Pharmaron (Ningbo) Technology Development Co., Ltd. No. 800 Bin-Hai 4th Road, Hangzhou Bay New Zone, Ningbo, 315336, China
| | - Xiaobing Yu
- Pharmaron (Ningbo) Technology Development Co., Ltd. No. 800 Bin-Hai 4th Road, Hangzhou Bay New Zone, Ningbo, 315336, China
| | - Kexin Yang
- Pharmaron Beijing Co., Ltd., 6 Taihe Road, BDA, Beijing, 100176, China
| | - Yun Jin Hu
- Pharmaron (Ningbo) Technology Development Co., Ltd. No. 800 Bin-Hai 4th Road, Hangzhou Bay New Zone, Ningbo, 315336, China
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7
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Cui K, Li YL, Li G, Xia JB. Regio- and Stereoselective Reductive Coupling of Alkynes and Crotononitrile. J Am Chem Soc 2022; 144:23001-23009. [DOI: 10.1021/jacs.2c10021] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Affiliation(s)
- Kun Cui
- State Key Laboratory for Oxo Synthesis and Selective Oxidation, Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences, Lanzhou 730000, China
- Institute of Advanced Materials, Jiangsu National Synergistic Innovation Center for Advanced Materials, Nanjing Tech University, Nanjing 21181, China
| | - Yan-Lin Li
- State Key Laboratory for Oxo Synthesis and Selective Oxidation, Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences, Lanzhou 730000, China
| | - Gongqiang Li
- Institute of Advanced Materials, Jiangsu National Synergistic Innovation Center for Advanced Materials, Nanjing Tech University, Nanjing 21181, China
| | - Ji-Bao Xia
- State Key Laboratory for Oxo Synthesis and Selective Oxidation, Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences, Lanzhou 730000, China
- University of Chinese Academy of Sciences, Beijing 100049, China
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8
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Thompson CV, Narro AL, Arman HD, Tonzetich ZJ. Synthesis and Reactivity of Iron(II) Acetylide Complexes Relevant to Alkyne Dimerization. Organometallics 2022. [DOI: 10.1021/acs.organomet.2c00265] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- C. Vance Thompson
- Department of Chemistry, University of Texas at San Antonio (UTSA), San Antonio, Texas 78249, United States
| | - Ana L. Narro
- Department of Chemistry, University of Texas at San Antonio (UTSA), San Antonio, Texas 78249, United States
| | - Hadi D. Arman
- Department of Chemistry, University of Texas at San Antonio (UTSA), San Antonio, Texas 78249, United States
| | - Zachary J. Tonzetich
- Department of Chemistry, University of Texas at San Antonio (UTSA), San Antonio, Texas 78249, United States
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9
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Wu K, Wu C, Jia XY, Zhou L, Li QH. Highly selective cross-coupling reactions of 1,1-dibromoethylenes with alkynylaluminums for the synthesis of aryl substituted conjugated enediynes and unsymmetrical 1,3-diynes. RSC Adv 2022; 12:13314-13318. [PMID: 35520111 PMCID: PMC9062886 DOI: 10.1039/d2ra02127g] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/02/2022] [Accepted: 04/25/2022] [Indexed: 11/21/2022] Open
Abstract
A highly efficient method for the synthesis of aryl substituted conjugated enediynes and unsymmetrical 1,3-diynes via selective cross-coupling reactions of 1,1-dibromoethylenes with alkynylaluminums using the Pd(OAc)2-DPPE and Pd2(dba)3-TFP complexes as catalysts, respectively, has been successfully developed. Though the alkyl substituted conjugated enediynes and unsymmetrical 1,3-diynes were not obtained, this case is also remarkable as the same starting materials could selectively produce either aryl substituted conjugated enediynes or unsymmetrical 1,3-diynes in moderate to excellent yields (up to 99%) in the different Pd-phosphine catalytic systems.
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Affiliation(s)
- Kun Wu
- Key Laboratory of General Chemistry of the National Ethnic Affairs Commission, College of Chemistry and Environment, Southwest Minzu University Chengdu 610041 P. R. China
| | - Chuan Wu
- Key Laboratory of General Chemistry of the National Ethnic Affairs Commission, College of Chemistry and Environment, Southwest Minzu University Chengdu 610041 P. R. China
| | - Xiao-Ying Jia
- Key Laboratory of General Chemistry of the National Ethnic Affairs Commission, College of Chemistry and Environment, Southwest Minzu University Chengdu 610041 P. R. China
| | - Lin Zhou
- Key Laboratory of General Chemistry of the National Ethnic Affairs Commission, College of Chemistry and Environment, Southwest Minzu University Chengdu 610041 P. R. China
| | - Qing-Han Li
- Key Laboratory of General Chemistry of the National Ethnic Affairs Commission, College of Chemistry and Environment, Southwest Minzu University Chengdu 610041 P. R. China
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10
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Guo H, Zhang S, Li Y, Yu X, Feng X, Yamamoto Y, Bao M. Palladium-Catalyzed Tail-to-Tail Reductive Dimerization of Terminal Alkynes to 2,3-Dibranched Butadienes. Angew Chem Int Ed Engl 2022; 61:e202116870. [PMID: 35103393 DOI: 10.1002/anie.202116870] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/10/2021] [Indexed: 11/05/2022]
Abstract
The palladium-catalyzed tail-to-tail reductive dimerization of terminal alkynes is described for the first time. Aromatic terminal alkynes bearing diverse and sensitive functional groups as well as aliphatic terminal alkynes are efficiently transformed to 2,3-dibranched butadienes. The key to achieve a selective tail-to-tail reductive dimerization reaction is to control appropriately the acidity of the reaction solution, which is accomplished by a combined use of pivalic acid and para-toluenesulfonic acid. The tail-to-tail reductive dimerization reaction is proposed to proceed via a cationic alkenyl palladium intermediate under acidic conditions.
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Affiliation(s)
- Hongyu Guo
- State Key Laboratory of Fine Chemicals, Dalian University of Technology, Dalian, 116023, China
| | - Sheng Zhang
- State Key Laboratory of Fine Chemicals, Dalian University of Technology, Dalian, 116023, China
| | - Yang Li
- State Key Laboratory of Fine Chemicals, Dalian University of Technology, Dalian, 116023, China
| | - Xiaoqiang Yu
- State Key Laboratory of Fine Chemicals, Dalian University of Technology, Dalian, 116023, China
| | - Xiujuan Feng
- State Key Laboratory of Fine Chemicals, Dalian University of Technology, Dalian, 116023, China
| | - Yoshinori Yamamoto
- State Key Laboratory of Fine Chemicals, Dalian University of Technology, Dalian, 116023, China.,Department of Chemistry, Tohoku University, Sendai, 980-8578, Japan
| | - Ming Bao
- State Key Laboratory of Fine Chemicals, Dalian University of Technology, Dalian, 116023, China
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11
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Guo H, Zhang S, Li Y, Yu X, Feng X, Yamamoto Y, Bao M. Palladium‐Catalyzed Tail‐to‐Tail Reductive Dimerization of Terminal Alkynes to 2,3‐Dibranched Butadienes. Angew Chem Int Ed Engl 2022. [DOI: 10.1002/ange.202116870] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Affiliation(s)
- Hongyu Guo
- State Key Laboratory of Fine Chemicals Dalian University of Technology Dalian 116023 China
| | - Sheng Zhang
- State Key Laboratory of Fine Chemicals Dalian University of Technology Dalian 116023 China
| | - Yang Li
- State Key Laboratory of Fine Chemicals Dalian University of Technology Dalian 116023 China
| | - Xiaoqiang Yu
- State Key Laboratory of Fine Chemicals Dalian University of Technology Dalian 116023 China
| | - Xiujuan Feng
- State Key Laboratory of Fine Chemicals Dalian University of Technology Dalian 116023 China
| | - Yoshinori Yamamoto
- State Key Laboratory of Fine Chemicals Dalian University of Technology Dalian 116023 China
- Department of Chemistry Tohoku University Sendai 980-8578 Japan
| | - Ming Bao
- State Key Laboratory of Fine Chemicals Dalian University of Technology Dalian 116023 China
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12
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Fan JT, Fan XH, Gao CY, Wei J, Yang LM. Regioselectively switchable alkyne cyclotrimerization catalyzed by the system of Ni(II)/bidentate P-ligand/Zn with ZnI 2 as additive. Org Chem Front 2022. [DOI: 10.1039/d1qo01913a] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
A simple catalyst system of Ni(PPh3)2Cl2/dppb or dppm/Zn can effect an efficient and regioselectively controlled alkyne cyclotrimerization to form 1,2,4- (with no additive) or 1,3,5-regioisomers (with the use of ZnI2...
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