1
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Zhu SJ, Hao ZF, Pan Y, Zhou Y, Liu XL, Zhang M, Lei CW. Asymmetric Formal (3 + 2) Cyclocondensation of Coumarin-3-Formylpyrazoles as 3-Carbon Partners with 3-Hydroxyoxindoles via Esterification/Michael Addition Sequence. J Org Chem 2022; 87:15210-15223. [PMID: 36305826 DOI: 10.1021/acs.joc.2c01757] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Abstract
The first enantioselective formal (3 + 2) cyclocondensation involving α,β-unsaturated pyrazoleamides as 3-carbon partners was accomplished in a stepwise fashion. The stepwise esterification/Michael addition sequence is promoted by Zn(OTf)2 and quinine-squaramide derivative, respectively. The protocol enables access to spiro-fused pentacyclic spirooxindoles from coumarin-3-formylpyrazoles and 3-hydroxyoxindoles in good to satisfactory overall yields (up to 91%) with excellent dr (all cases >20:1 dr) and high ee values (up to 99%). Mechanistic investigations contributed to shedding light on the enantioselective event of the process.
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Affiliation(s)
- Shi-Jie Zhu
- School of Pharmacy, Guizhou University of Traditional Chinese Medicine, Guiyang 550025, P. R. China
| | - Zhi-Feng Hao
- School of Pharmacy, Guizhou University of Traditional Chinese Medicine, Guiyang 550025, P. R. China
| | - Ya Pan
- School of Pharmacy, Guizhou University of Traditional Chinese Medicine, Guiyang 550025, P. R. China
| | - Ying Zhou
- School of Pharmacy, Guizhou University of Traditional Chinese Medicine, Guiyang 550025, P. R. China
| | - Xiong-Li Liu
- National and Local Joint Engineering Research Center for the Exploitation of Homology Resources of Medicine and Food, Guizhou University, Guiyang 550025, P. R. China
| | - Ming Zhang
- National and Local Joint Engineering Research Center for the Exploitation of Homology Resources of Medicine and Food, Guizhou University, Guiyang 550025, P. R. China
| | - Chuan-Wen Lei
- School of Pharmacy, Guizhou University of Traditional Chinese Medicine, Guiyang 550025, P. R. China
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2
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Fang G, Wang H, Zheng C, Pan L, Zhao G. Enantioselectivity switch in asymmetric Michael addition reactions using phosphonium salts. Org Biomol Chem 2021; 19:6334-6340. [PMID: 34231639 DOI: 10.1039/d1ob01027a] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
Efficient access to two enantiomers of one chiral compound is critical for the discovery of drugs. However, it is still a challenging problem owing to the difficulty in obtaining two enantiomers of one chiral catalyst. Here, we report a general method to obtain both enantiomeric products via fine tuning the hydrogen-bonding interactions of phosphonium salts. Amino acid derived phosphonium salts and dipeptide derived phosphonium salts exhibited different properties for controlling the transition state, which could efficiently promote the Michael addition reaction to give opposite configurations of products with high yields and enantioselectivities. Preliminary investigations on the mechanism of the reaction and applications of the products were also performed.
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Affiliation(s)
- Guosheng Fang
- Department of Chemistry, University of Science and Technology of China, Hefei 230026, Anhui, China.
| | - Hongyu Wang
- Center for Excellence in Molecular Synthesis, Key Laboratory of Synthetic Chemistry of Natural Substances, Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences, 345 LingLing Road, Shanghai 200032, China
| | - Changwu Zheng
- Center for Excellence in Molecular Synthesis, Key Laboratory of Synthetic Chemistry of Natural Substances, Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences, 345 LingLing Road, Shanghai 200032, China
| | - Lu Pan
- Center for Excellence in Molecular Synthesis, Key Laboratory of Synthetic Chemistry of Natural Substances, Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences, 345 LingLing Road, Shanghai 200032, China
| | - Gang Zhao
- Department of Chemistry, University of Science and Technology of China, Hefei 230026, Anhui, China. and Center for Excellence in Molecular Synthesis, Key Laboratory of Synthetic Chemistry of Natural Substances, Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences, 345 LingLing Road, Shanghai 200032, China
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3
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Meninno S, Franco F, Benaglia M, Lattanzi A. Pyrazoleamides in Catalytic Asymmetric Reactions: Recent Advances. Adv Synth Catal 2021. [DOI: 10.1002/adsc.202100006] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/15/2023]
Affiliation(s)
- Sara Meninno
- Dipartimento di Chimica e Biologia “A. Zambelli” Università di Salerno Via Giovanni Paolo II 132 84084 Fisciano Italy
| | - Francesca Franco
- Dipartimento di Chimica e Biologia “A. Zambelli” Università di Salerno Via Giovanni Paolo II 132 84084 Fisciano Italy
| | - Maurizio Benaglia
- Dipartimento di Chimica Università degli Studi di Milano Via Golgi 19 20133 Milano Italy
| | - Alessandra Lattanzi
- Dipartimento di Chimica e Biologia “A. Zambelli” Università di Salerno Via Giovanni Paolo II 132 84084 Fisciano Italy
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4
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Curran SP, Fallon BJ, Connon SJ. C
2
‐Symmetric Cinchona Alkaloid Derivatives: Versatile Catalysts for the Enantioselective C−C Bond Forming Conjugate Addition of Nucleophiles to Simple α,β‐Unsaturated Acyl Pyrazoles. ChemistrySelect 2020. [DOI: 10.1002/slct.202004505] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Affiliation(s)
- Simon P. Curran
- School of Chemistry Trinity Biomedical Sciences Institute Trinity College Dublin 152-160 Pearse Street 2 Dublin Ireland
| | - Brendan J. Fallon
- School of Chemistry Trinity Biomedical Sciences Institute Trinity College Dublin 152-160 Pearse Street 2 Dublin Ireland
| | - Stephen J. Connon
- School of Chemistry Trinity Biomedical Sciences Institute Trinity College Dublin 152-160 Pearse Street 2 Dublin Ireland
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5
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Xian J, Chen L, Ye L, Sun Y, Shi Z, Zhao Z, Li X. Enantioselective synthesis of fused dihydropyranones via squaramide-catalyzed Michael addition/lactonization cascade reaction. Tetrahedron 2019. [DOI: 10.1016/j.tet.2019.03.007] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
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6
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Liu Y, Ye L, Shi Z, Yang X, Zhao Z, Li X. Highly enantioselective Michael addition of α-nitroacetate to α,β-unsaturated pyrazolamide catalyzed by a bifunctional squaramide. Chirality 2018; 30:1287-1303. [PMID: 30286255 DOI: 10.1002/chir.23023] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/27/2018] [Revised: 05/20/2018] [Accepted: 08/30/2018] [Indexed: 01/03/2023]
Abstract
A highly enantioselective (91- > 99% ee) Michael addition of α-nitroacetate to α,β-unsaturated pyrazolamide was developed in the presence of a bifunctional squaramide. Satisfactory isolated yields (42%-99%) have been achieved with a wide range of α,β-unsaturated pyrazolamides, albeit acceptor of this type displayed poor reactivity in the precedent reports. The adducts resulting from this protocol are useful synthetic intermediates for further synthetic modification.
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Affiliation(s)
- Yingying Liu
- College of Chemistry and Environment Protection Engineering, Southwest Minzu University, Chengdu, China
| | - Ling Ye
- Faculty of Geosciences and Environmental Engineering, Southwest Jiaotong University, Chengdu, China
| | - Zhichuan Shi
- College of Chemistry and Environment Protection Engineering, Southwest Minzu University, Chengdu, China
| | - Xuejun Yang
- College of Chemistry and Environment Protection Engineering, Southwest Minzu University, Chengdu, China
| | - Zhigang Zhao
- College of Chemistry and Environment Protection Engineering, Southwest Minzu University, Chengdu, China
| | - Xuefeng Li
- College of Chemistry and Environment Protection Engineering, Southwest Minzu University, Chengdu, China
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7
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Hayama N, Kuramoto R, Földes T, Nishibayashi K, Kobayashi Y, Pápai I, Takemoto Y. Mechanistic Insight into Asymmetric Hetero-Michael Addition of α,β-Unsaturated Carboxylic Acids Catalyzed by Multifunctional Thioureas. J Am Chem Soc 2018; 140:12216-12225. [PMID: 30215516 DOI: 10.1021/jacs.8b07511] [Citation(s) in RCA: 56] [Impact Index Per Article: 9.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
Carboxylic acids and their corresponding carboxylate anions are generally utilized as Brønsted acids/bases and oxygen nucleophiles in organic synthesis. However, a few asymmetric reactions have used carboxylic acids as electrophiles. Although chiral thioureas bearing both arylboronic acid and tertiary amine were found to promote the aza-Michael addition of BnONH2 to α,β-unsaturated carboxylic acids with moderate to good enantioselectivities, the reaction mechanism remains to be clarified. Detailed investigation of the reaction using spectroscopic analysis and kinetic studies identified tetrahedral borate complexes, comprising two carboxylate anions, as reaction intermediates. We realized a dramatic improvement in product enantioselectivity with the addition of 1 equiv of benzoic acid. In this aza-Michael reaction, the boronic acid not only activates the carboxylate ligand as a Lewis acid, together with the thiourea NH-protons, but also functions as a Brønsted base through a benzoyloxy anion to activate the nucleophile. Moreover, molecular sieves were found to play an important role in generating the ternary borate complexes, which were crucial for obtaining high enantioselectivity as demonstrated by DFT calculations. We also designed a new thiourea catalyst for the intramolecular oxa-Michael addition to suppress another catalytic pathway via a binary borate complex using steric hindrance between the catalyst and substrate. Finally, to demonstrate the synthetic versatility of both hetero-Michael additions, we used them to accomplish the asymmetric synthesis of key intermediates in pharmaceutically important molecules, including sitagliptin and α-tocopherol.
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Affiliation(s)
- Noboru Hayama
- Graduate School of Pharmaceutical Sciences , Kyoto University , Yoshida, Sakyo-ku, Kyoto 606-8501 , Japan
| | - Ryuta Kuramoto
- Graduate School of Pharmaceutical Sciences , Kyoto University , Yoshida, Sakyo-ku, Kyoto 606-8501 , Japan
| | - Tamás Földes
- Institute of Organic Chemistry, Research Centre for Natural Sciences , Hungarian Academy of Sciences , Magyar tudósok körútja 2 , H-1117 Budapest , Hungary
| | - Kazuya Nishibayashi
- Graduate School of Pharmaceutical Sciences , Kyoto University , Yoshida, Sakyo-ku, Kyoto 606-8501 , Japan
| | - Yusuke Kobayashi
- Graduate School of Pharmaceutical Sciences , Kyoto University , Yoshida, Sakyo-ku, Kyoto 606-8501 , Japan
| | - Imre Pápai
- Institute of Organic Chemistry, Research Centre for Natural Sciences , Hungarian Academy of Sciences , Magyar tudósok körútja 2 , H-1117 Budapest , Hungary
| | - Yoshiji Takemoto
- Graduate School of Pharmaceutical Sciences , Kyoto University , Yoshida, Sakyo-ku, Kyoto 606-8501 , Japan
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8
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Ray SK, Biswas RG, Suneja A, Sadhu MM, Singh VK. (R)-DM-SEGPHOS-Ag(I)-Catalyzed Enantioselective Synthesis of Pyrrolidines and Pyrrolizidines via (1,3)- and Double (1,3)-Dipolar Cycloaddition Reactions. J Org Chem 2018; 83:2293-2308. [PMID: 29364672 DOI: 10.1021/acs.joc.7b03185] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
An efficient diastereo- and enantioselective route to access a wide range of highly substituted pyrrolidine and pyrrolizidine derivatives has been described via (1,3)- and double (1,3)-dipolar cycloaddition reactions catalyzed by the (R)-DM-SEGPHOS-Ag(I) complex. The reactions proceed smoothly at ambient temperature, affording a variety of pyrrolidines and pyrrolizidines in high yields (up to 93%) with up to 99:1 dr and excellent enantioselectivities (up to 98% ee) without any additives. The newly synthesized pyrrolidine and pyrrolizidine derivatives contain four and seven contiguous stereogenic centers, respectively. Moreover, the synthetic utility of enantioenriched products has been demonstrated by transforming them into various synthetically useful advanced intermediates.
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Affiliation(s)
- Sumit K Ray
- Department of Chemistry, Indian Institute of Science Education and Research Bhopal , Bhopal, Madhya Pradesh 462 066, India
| | - Rayhan G Biswas
- Department of Chemistry, Indian Institute of Science Education and Research Bhopal , Bhopal, Madhya Pradesh 462 066, India
| | - Arun Suneja
- Department of Chemistry, Indian Institute of Science Education and Research Bhopal , Bhopal, Madhya Pradesh 462 066, India
| | - Milon M Sadhu
- Department of Chemistry, Indian Institute of Science Education and Research Bhopal , Bhopal, Madhya Pradesh 462 066, India
| | - Vinod K Singh
- Department of Chemistry, Indian Institute of Science Education and Research Bhopal , Bhopal, Madhya Pradesh 462 066, India.,Department of Chemistry, Indian Institute of Technology Kanpur , Kanpur, Uttar Pradesh 208 016, India
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9
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Wang Q, Wang W, Ye L, Yang X, Li X, Zhao Z, Li X. Enantioselective Michael Addition of Cyclic β-Diones to α,β-Unsaturated Enones Catalyzed by Quinine-Based Organocatalysts. Molecules 2017; 22:molecules22071096. [PMID: 28665357 PMCID: PMC6152274 DOI: 10.3390/molecules22071096] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/16/2017] [Revised: 06/25/2017] [Accepted: 06/26/2017] [Indexed: 12/28/2022] Open
Abstract
An enantioselective (52–98% ee) Michael addition between cyclic β-diones and α,β-unsaturated enones was established in the presence of quinine-based primary amine or squaramide. A variety of cinnamones were smoothly converted into the desired 3,4-dihydropyrans in moderate to high yields (63–99%). Chalcones were also suitable acceptors and gave rise to the expected adducts in satisfactory yields (31–99%). The resulting adducts readily underwent further modification to form fused 4H-pyran or 2,3-dihydrofuran.
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Affiliation(s)
- Qingqing Wang
- College of Chemistry and Environment Protection Engineering, Southwest Minzu University, Chengdu 610041, China.
| | - Wei Wang
- College of Chemistry and Environment Protection Engineering, Southwest Minzu University, Chengdu 610041, China.
| | - Ling Ye
- Faculty of Geosciences and Environmental Engineering, Southwest Jiaotong University, Chengdu 610031, China.
| | - Xuejun Yang
- College of Chemistry and Environment Protection Engineering, Southwest Minzu University, Chengdu 610041, China.
| | - Xinying Li
- College of Chemistry and Environment Protection Engineering, Southwest Minzu University, Chengdu 610041, China.
| | - Zhigang Zhao
- College of Chemistry and Environment Protection Engineering, Southwest Minzu University, Chengdu 610041, China.
| | - Xuefeng Li
- College of Chemistry and Environment Protection Engineering, Southwest Minzu University, Chengdu 610041, China.
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10
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Zhang HJ, Shi CY, Zhong F, Yin L. Direct Asymmetric Vinylogous and Bisvinylogous Mannich-Type Reaction Catalyzed by a Copper(I) Complex. J Am Chem Soc 2017; 139:2196-2199. [DOI: 10.1021/jacs.6b13042] [Citation(s) in RCA: 52] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Hai-Jun Zhang
- CAS Key Laboratory of Synthetic
Chemistry of Natural Substances, Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences, 345 Lingling Road, Shanghai 200032, China
| | - Chang-Yun Shi
- CAS Key Laboratory of Synthetic
Chemistry of Natural Substances, Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences, 345 Lingling Road, Shanghai 200032, China
| | - Feng Zhong
- CAS Key Laboratory of Synthetic
Chemistry of Natural Substances, Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences, 345 Lingling Road, Shanghai 200032, China
| | - Liang Yin
- CAS Key Laboratory of Synthetic
Chemistry of Natural Substances, Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences, 345 Lingling Road, Shanghai 200032, China
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11
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Zhang G, Zhu C, Liu D, Pan J, Zhang J, Hu D, Song B. Solvent-free enantioselective conjugate addition and bioactivities of nitromethane to Chalcone containing pyridine. Tetrahedron 2017. [DOI: 10.1016/j.tet.2016.11.063] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
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12
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Wang G, Tang Y, Zhang Y, Liu X, Lin L, Feng X. Enantioselective Synthesis of N-H-Free 1,5-Benzothiazepines. Chemistry 2016; 23:554-557. [PMID: 27862459 DOI: 10.1002/chem.201605127] [Citation(s) in RCA: 38] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/03/2016] [Indexed: 11/10/2022]
Abstract
An enantioselective sulfa-Michael-cyclization reaction was developed for the synthesis of 1,5-benzothiazepines with versatile pharmacological activities. The reaction between 2-aminothiophenol and α,β-unsaturated pyrazoleamides gave direct access to N-H-free 1,5-benzothiazepines in the presence of a chiral N,N'-dioxide/Yb(OTf)3 complex. Excellent enantioselectivities (up to 96 % ee) and high yields (up to 99 %) were obtained for a broad range of substrates under mild reaction conditions. This method provided a facile approach to the antidepressant drug (R)-(-)-Thiazesim.
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Affiliation(s)
- Guojin Wang
- Key Laboratory of Green Chemistry and Technology, Ministry of Education, College of Chemistry, Sichuan University, Chengdu, 610064, P.R. China
| | - Yu Tang
- Key Laboratory of Green Chemistry and Technology, Ministry of Education, College of Chemistry, Sichuan University, Chengdu, 610064, P.R. China
| | - Yu Zhang
- Key Laboratory of Green Chemistry and Technology, Ministry of Education, College of Chemistry, Sichuan University, Chengdu, 610064, P.R. China
| | - Xiaohua Liu
- Key Laboratory of Green Chemistry and Technology, Ministry of Education, College of Chemistry, Sichuan University, Chengdu, 610064, P.R. China
| | - Lili Lin
- Key Laboratory of Green Chemistry and Technology, Ministry of Education, College of Chemistry, Sichuan University, Chengdu, 610064, P.R. China
| | - Xiaoming Feng
- Key Laboratory of Green Chemistry and Technology, Ministry of Education, College of Chemistry, Sichuan University, Chengdu, 610064, P.R. China
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13
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Cui L, Wang Y, Zhou Z. Enantioselective synthesis of 7H-pyrano[2,3-d]thiazoles via squaramide-catalyzed [2+4] annulation of malononitrile and 5-ylidenethiazol-4-ones. ACTA ACUST UNITED AC 2016. [DOI: 10.1016/j.tetasy.2016.08.014] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
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14
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Zhang Y, Liao Y, Liu X, Yao Q, Zhou Y, Lin L, Feng X. Catalytic Michael/Ring-Closure Reaction of α,β-Unsaturated Pyrazoleamides with Amidomalonates: Asymmetric Synthesis of (-)-Paroxetine. Chemistry 2016; 22:15119-15124. [PMID: 27576747 DOI: 10.1002/chem.201603056] [Citation(s) in RCA: 36] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/27/2016] [Indexed: 12/12/2022]
Abstract
A highly enantioselective tandem Michael/ring-closure reaction of α,β-unsaturated pyrazoleamides and amidomalonates has been accomplished in the presence of a chiral N,N'-dioxide-Yb(OTf)3 complex (Tf: trifluoromethanesulfonyl) to give various substituted chiral glutarimides with high yields and diastereo- and enantioselectivities. Moreover, this methodology could be used for gram-scale manipulation and was successfully applied to the synthesis of (-)-paroxetine. Further nonlinear and HRMS studies revealed that the real catalytically active species was a monomeric L-PMe2 -Yb3+ complex. A plausible transition state was proposed to explain the origin of the asymmetric induction.
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Affiliation(s)
- Yu Zhang
- Key Laboratory of Green Chemistry & Technology, Ministry of Education, College of Chemistry, Sichuan University, Chengdu, 610064, P.R. China), Fax: (+86) 28 8541 8249
| | - Yuting Liao
- Key Laboratory of Green Chemistry & Technology, Ministry of Education, College of Chemistry, Sichuan University, Chengdu, 610064, P.R. China), Fax: (+86) 28 8541 8249
| | - Xiaohua Liu
- Key Laboratory of Green Chemistry & Technology, Ministry of Education, College of Chemistry, Sichuan University, Chengdu, 610064, P.R. China), Fax: (+86) 28 8541 8249.
| | - Qian Yao
- Key Laboratory of Green Chemistry & Technology, Ministry of Education, College of Chemistry, Sichuan University, Chengdu, 610064, P.R. China), Fax: (+86) 28 8541 8249
| | - Yuhang Zhou
- Key Laboratory of Green Chemistry & Technology, Ministry of Education, College of Chemistry, Sichuan University, Chengdu, 610064, P.R. China), Fax: (+86) 28 8541 8249
| | - Lili Lin
- Key Laboratory of Green Chemistry & Technology, Ministry of Education, College of Chemistry, Sichuan University, Chengdu, 610064, P.R. China), Fax: (+86) 28 8541 8249
| | - Xiaoming Feng
- Key Laboratory of Green Chemistry & Technology, Ministry of Education, College of Chemistry, Sichuan University, Chengdu, 610064, P.R. China), Fax: (+86) 28 8541 8249.
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15
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A general, highly enantioselective Michael addition of nitroalkanes to α,β-unsaturated enones catalyzed by 9-amino(9-deoxy)-epi-quinine: a remarkable additive effect. Tetrahedron 2016. [DOI: 10.1016/j.tet.2016.07.008] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
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