1
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Pasturaud K, Rkein B, Sanselme M, Sebban M, Lakhdar S, Durandetti M, Legros J, Chataigner I. The facile dearomatization of nitroaromatic compounds using lithium enolates of unsaturated ketones in conjugate additions and (4+2) formal cycloadditions. Chem Commun (Camb) 2019; 55:7494-7497. [PMID: 31185071 DOI: 10.1039/c9cc02924a] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
The dearomatization of conventional nitroarenes by lithiated enolates derived from methyl vinyl ketones easily takes place, following a formal (4+2) cycloaddition process. While nitroindoles react readily with in situ generated conjugated enolates, the deaggregation of these latter species using HMPA extends the reaction scope to the more aromatic nitronaphthalenes and pyridines.
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Affiliation(s)
- Karine Pasturaud
- Normandie Univ., UNIROUEN, INSA Rouen, CNRS, COBRA, 76000 Rouen, France.
| | - Batoul Rkein
- Normandie Univ., UNIROUEN, INSA Rouen, CNRS, COBRA, 76000 Rouen, France.
| | | | - Muriel Sebban
- Normandie Univ., UNIROUEN, INSA Rouen, CNRS, COBRA, 76000 Rouen, France.
| | - Sami Lakhdar
- Normandie Univ., LCMT, ENSICAEN, UNICAEN, CNRS, 6, Boulevard Maréchal Juin, Caen 14000, France
| | - Muriel Durandetti
- Normandie Univ., UNIROUEN, INSA Rouen, CNRS, COBRA, 76000 Rouen, France.
| | - Julien Legros
- Normandie Univ., UNIROUEN, INSA Rouen, CNRS, COBRA, 76000 Rouen, France.
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2
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Abstract
The solution structures, stabilities, physical properties, and reactivities of sodium diisopropylamide (NaDA) in a variety of coordinating solvents are described. NaDA is stable for months as a solid or as a 1.0 M solution in N,N-dimethylethylamine (DMEA) at -20 °C. A combination of NMR spectroscopic and computational studies show that NaDA is a disolvated symmetric dimer in DMEA, N,N-dimethyl-n-butylamine, and N-methylpyrrolidine. Tetrahydrofuran (THF) readily displaces DMEA, affording a tetrasolvated cyclic dimer at all THF concentrations. Dimethoxyethane (DME) and N,N,N',N'-tetramethylethylenediamine quantitatively displace DMEA, affording doubly chelated symmetric dimers. The trifunctional ligands N,N,N',N″,N″-pentamethyldiethylenetriamine and diglyme bind the dimer as bidentate rather than tridentate ligands. Relative rates of solvent decompositions are reported, and rate studies for the decomposition of THF and DME are consistent with monomer-based mechanisms.
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Affiliation(s)
- Russell F. Algera
- Department of Chemistry and Chemical Biology, Baker Laboratory, Cornell University, Ithaca, New York 14853–1301, United States,
| | - Yun Ma
- Department of Chemistry and Chemical Biology, Baker Laboratory, Cornell University, Ithaca, New York 14853–1301, United States,
| | - David B. Collum
- Department of Chemistry and Chemical Biology, Baker Laboratory, Cornell University, Ithaca, New York 14853–1301, United States,
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3
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Marchois J, Fressigné C, Lecachey B, Maddaluno J. Base or nucleophile? DFT finally elucidates the origin of the selectivity between the competitive reactions triggered by MeLi or LDA on propanal. Chem Commun (Camb) 2015; 51:9801-4. [PMID: 25925129 DOI: 10.1039/c5cc01549a] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The competition between basicity and nucleophilicity of two standard organolithium reagents was studied using DFT. Comparing the reactivity of solvated (MeLi)2 and (LDA)2 toward propanal finally explains why methyllithium adds onto the carbonyl while LDA deprotonates the α-position, in accord with experiment and Ireland's deprotonation TS.
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Affiliation(s)
- J Marchois
- Laboratoire COBRA, CNRS UMR 6014 & FR 3038, Université de Rouen and INSA de Rouen, 76821-Mont St Aignan Cedex, France.
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4
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Guang J, Liu QP, Hopson R, Williard PG. Lithium pinacolone enolate solvated by hexamethylphosphoramide. J Am Chem Soc 2015; 137:7347-56. [PMID: 25933508 DOI: 10.1021/jacs.5b01906] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
We report the crystal structure of a substoichiometric, HMPA-trisolvated lithium pinacolone enolate tetramer (LiOPin)4·HMPA3 abbreviated as T3. In this tetramer one HMPA binds to lithium more strongly than the other two causing a reduction in spatial symmetry with corresponding loss of C3 symmetry. A variety of NMR experiments, including HMPA titration, diffusion coefficient-formula weight (D-FW) analysis, and other multinuclear one- and two-dimensional NMR techniques reveal that T3 is the major species in hydrocarbon solution when more than 0.6 equiv of HMPA is present. Due to a small amount of moisture from HMPA or air leaking into the solution, a minor complex was identified and confirmed by X-ray diffraction analysis as a mixed aggregate containing enolate, lithium hydroxide, and HMPA in a 4:2:4 ratio, [(LiOPin)4·(LiOH)2·HMPA4], that we refer to as pseudo-T4. A tetra-HMPA-solvated lithium cyclopentanone enolate tetramer was also prepared and characterized by X-ray diffraction, leading to the conclusion that steric effects dominate the formation and solvation of the pinacolone aggregates. An unusual mixed aggregate consisting of pinacolone enolate, lithium diisopropyl amide, lithium oxide, and HMPA in the ratio 5:1:1:2 is also described.
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Affiliation(s)
- Jie Guang
- Department of Chemistry, Brown University, Providence, Rhode Island 02912, United States
| | - Qiyong Peter Liu
- Department of Chemistry, Brown University, Providence, Rhode Island 02912, United States
| | - Russell Hopson
- Department of Chemistry, Brown University, Providence, Rhode Island 02912, United States
| | - Paul G Williard
- Department of Chemistry, Brown University, Providence, Rhode Island 02912, United States
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5
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Kerr WJ, Lindsay DM, Patel VK, Rajamanickam M. Efficient methods for enol phosphate synthesis using carbon-centred magnesium bases. Org Biomol Chem 2015; 13:10131-5. [DOI: 10.1039/c5ob01849h] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Abstract
Efficient conversion of ketones into enol phosphates under mild and accessible conditions has been realised using the developed methods with di-tert-butylmagnesium and bismesitylmagnesium. Optimisation of the quench protocol resulted in high yields of enol phosphates from a range of cyclohexanones and aryl methyl ketones.
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Affiliation(s)
- William J. Kerr
- Department of Pure and Applied Chemistry
- WestCHEM
- University of Strathclyde
- Glasgow
- UK
| | - David M. Lindsay
- Department of Pure and Applied Chemistry
- WestCHEM
- University of Strathclyde
- Glasgow
- UK
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Yamagami T, Moriyama N, Kyuhara M, Moroda A, Uemura T, Matsumae H, Moritani Y, Inoue I. Scalable Synthesis of a Nonracemic α-Arylpropionic Acid via Ketene Desymmetrization for a Glucokinase Activator. Org Process Res Dev 2014. [DOI: 10.1021/op400354g] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Takafumi Yamagami
- Process Chemistry Research
Laboratories, CMC Division, Mitsubishi Tanabe Pharma Corporation, 3-16-89, Kashima, Yodogawa-ku, Osaka 532-8505, Japan
| | - Noriaki Moriyama
- Process Chemistry Research
Laboratories, CMC Division, Mitsubishi Tanabe Pharma Corporation, 3-16-89, Kashima, Yodogawa-ku, Osaka 532-8505, Japan
| | - Masahiro Kyuhara
- Process Chemistry Research
Laboratories, CMC Division, Mitsubishi Tanabe Pharma Corporation, 3-16-89, Kashima, Yodogawa-ku, Osaka 532-8505, Japan
| | - Atsushi Moroda
- Process Chemistry Research
Laboratories, CMC Division, Mitsubishi Tanabe Pharma Corporation, 3-16-89, Kashima, Yodogawa-ku, Osaka 532-8505, Japan
| | - Takeshi Uemura
- Process Chemistry Research
Laboratories, CMC Division, Mitsubishi Tanabe Pharma Corporation, 3-16-89, Kashima, Yodogawa-ku, Osaka 532-8505, Japan
| | - Hiroaki Matsumae
- Process Chemistry Research
Laboratories, CMC Division, Mitsubishi Tanabe Pharma Corporation, 3-16-89, Kashima, Yodogawa-ku, Osaka 532-8505, Japan
| | - Yasunori Moritani
- Process Chemistry Research
Laboratories, CMC Division, Mitsubishi Tanabe Pharma Corporation, 3-16-89, Kashima, Yodogawa-ku, Osaka 532-8505, Japan
| | - Isao Inoue
- Process Chemistry Research
Laboratories, CMC Division, Mitsubishi Tanabe Pharma Corporation, 3-16-89, Kashima, Yodogawa-ku, Osaka 532-8505, Japan
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7
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Su C, Guang J, Williard PG. Structures of Lithium N-Monosubstituted Anilides: Trisolvated Monomer to Tetrasolvated Dimer. J Org Chem 2014; 79:1032-9. [DOI: 10.1021/jo402498z] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Affiliation(s)
- Chicheung Su
- Department of Chemistry, Brown University, Providence, Rhode Island 02912, United States
| | - Jie Guang
- Department of Chemistry, Brown University, Providence, Rhode Island 02912, United States
| | - Paul G. Williard
- Department of Chemistry, Brown University, Providence, Rhode Island 02912, United States
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9
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Larrañaga O, de Cózar A, Bickelhaupt FM, Zangi R, Cossío FP. Aggregation and cooperative effects in the aldol reactions of lithium enolates. Chemistry 2013; 19:13761-73. [PMID: 23964002 DOI: 10.1002/chem.201301597] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/25/2013] [Indexed: 11/11/2022]
Abstract
Density functional theory and Car-Parrinello molecular dynamics simulations have been carried out for model aldol reactions involving aggregates of lithium enolates derived from acetaldehyde and acetone. Formaldehyde and acetone have been used as electrophiles. It is found that the geometries of the enolate aggregates are in general determined by the most favorable arrangements of the point charges within the respective Lin On clusters. The reactivity of the enolates follows the sequence monomer≫dimer>tetramer. In lithium aggregates, the initially formed aldol adducts must rearrange to form more stable structures in which the enolate and alkoxide oxygen atoms are within the respective Lin On clusters. Positive cooperative effects, similar to allosteric effects found in several proteins, are found for the successive aldol reactions in aggregates. The corresponding transition structures show in general sofa geometries.
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Affiliation(s)
- Olatz Larrañaga
- Departamento de Química Orgánica I/, Kimika Organikoa I Saila, Facultad de Química/, Kimika Fakultatea Euskal Herriko Unibertsitatea, UPV/EHU and Donostia International Physics Center (DIPC), 1072, 20018 San Sebastián-Donostia (Spain)
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10
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Harrison-Marchand A, Mongin F. Mixed AggregAte (MAA): A Single Concept for All Dipolar Organometallic Aggregates. 1. Structural Data. Chem Rev 2013; 113:7470-562. [DOI: 10.1021/cr300295w] [Citation(s) in RCA: 145] [Impact Index Per Article: 13.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Anne Harrison-Marchand
- Laboratoire COBRA de l′Université de Rouen, INSA de Rouen, CNRS, UMR 6014 & FR 3038, IRCOF, Rue Tesnière, 76821 Mont St Aignan Cédex, France
| | - Florence Mongin
- Équipe Chimie et Photonique Moléculaires, Institut des Sciences Chimiques de Rennes, UMR 6226 CNRS-Université de Rennes 1, Bâtiment 10A, case 1003, Avenue du Général Leclerc, 35042 Rennes Cédex, France
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11
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Chisholm MH, Choojun K, Chow AS, Fraenkel G. Molecular Dynamics and Ligand Exchange in Magnesium Complexes: Evidence for both Dissociative and Associative Ligand Exchange. Angew Chem Int Ed Engl 2013; 52:3264-6. [DOI: 10.1002/anie.201209542] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/28/2012] [Indexed: 11/06/2022]
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12
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Chisholm MH, Choojun K, Chow AS, Fraenkel G. Molecular Dynamics and Ligand Exchange in Magnesium Complexes: Evidence for both Dissociative and Associative Ligand Exchange. Angew Chem Int Ed Engl 2013. [DOI: 10.1002/ange.201209542] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
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13
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Prestly MR, Simpkins NS. Chiral Bases as Useful Probes of Lithium Amide Reactivity. Angew Chem Int Ed Engl 2012. [DOI: 10.1002/ange.201206558] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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14
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Prestly MR, Simpkins NS. Chiral Bases as Useful Probes of Lithium Amide Reactivity. Angew Chem Int Ed Engl 2012; 51:12068-71. [DOI: 10.1002/anie.201206558] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/14/2012] [Indexed: 11/07/2022]
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15
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Abstract
The lithiation and electrophilic substitution of dimethyl triazones is described. Directed lithiation or tin-lithium exchange of dimethyl triazones afforded the corresponding dipole stabilized nucleophiles that were trapped with various electrophiles. Keto-triazone derivatives accessed by acylation of such nucleophiles were readily converted to the corresponding imidazolone heterocycles.
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16
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Tilly D, Magolan J, Mortier J. Directed Remote Aromatic Metalations: Mechanisms and Driving Forces. Chemistry 2012; 18:3804-20. [DOI: 10.1002/chem.201103920] [Citation(s) in RCA: 55] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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Kolonko KJ, Wherritt DJ, Reich HJ. Mechanistic studies of the lithium enolate of 4-fluoroacetophenone: rapid-injection NMR study of enolate formation, dynamics, and aldol reactivity. J Am Chem Soc 2011; 133:16774-7. [PMID: 21939211 DOI: 10.1021/ja207218f] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Lithium enolates are widely used nucleophiles with a complicated and only partially understood solution chemistry. Deprotonation of 4-fluoroacetophenone in THF with lithium diisopropylamide occurs through direct reaction of the amide dimer to yield a mixed enolate-amide dimer (3), then an enolate homodimer (1-Li)(2), and finally an enolate tetramer (1-Li)(4), the equilibrium structure. Aldol reactions of both the metastable dimer and the stable tetramer of the enolate were investigated. Each reacted directly with the aldehyde to give a mixed enolate-aldolate aggregate, with the dimer only about 20 times as reactive as the tetramer at -120 °C.
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Affiliation(s)
- Kristopher J Kolonko
- Department of Chemistry, University of Wisconsin, 1101 University Avenue, Madison, Wisconsin 53706, USA
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Araoz R, Servent D, Molgó J, Iorga BI, Fruchart-Gaillard C, Benoit E, Gu Z, Stivala C, Zakarian A. Total synthesis of pinnatoxins A and G and revision of the mode of action of pinnatoxin A. J Am Chem Soc 2011; 133:10499-511. [PMID: 21644584 PMCID: PMC3365589 DOI: 10.1021/ja201254c] [Citation(s) in RCA: 104] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Pinnatoxins belong to an emerging class of potent marine toxins of the cyclic imine group. Detailed studies of their biological effects have been impeded by unavailability of the complex natural product from natural sources. This work describes the development of a robust, scalable synthetic sequence relying on a convergent strategy that delivered a sufficient amount of the toxin for detailed biological studies and its commercialization for use by other research groups and regulatory agencies. A central transformation in the synthesis is the highly diastereoselective Ireland-Claisen rearrangement of a complex α,α-disubstituted allylic ester based on a unique mode for stereoselective enolization through a chirality match between the substrate and the lithium amide base. With synthetic pinnatoxin A, a detailed study has been performed that provides conclusive evidence for its mode of action as a potent inhibitor of nicotinic acetylcholine receptors selective for the human neuronal α7 subtype. The comprehensive electrophysiological, biochemical, and computational studies support the view that the spiroimine subunit of pinnatoxins is critical for blocking nicotinic acetylcholine receptor subtypes, as evidenced by analyzing the effect of a synthetic analogue of pinnatoxin A containing an open form of the imine ring. Our studies have paved the way for the production of certified standards to be used for mass-spectrometric determination of these toxins in marine matrices and for the development of tests to detect these toxins in contaminated shellfish.
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Affiliation(s)
- Romulo Araoz
- Institut de Neurobiologie Alfred Fessard, FRC2118, Laboratoire de Neurobiologie et Développement, UPR-3294, Centre National de la Recherche Scientifique, F-91198 Gif-sur-Yvette cedex, France
| | - Denis Servent
- Service d'Ingénierie Moléculaire des Protéines, Laboratoire de Toxinologie Moléculaire et Biotechnologies, Commissariat à l'Energie Atomique, F-91191 Gif-sur-Yvette, France
| | - Jordi Molgó
- Institut de Neurobiologie Alfred Fessard, FRC2118, Laboratoire de Neurobiologie et Développement, UPR-3294, Centre National de la Recherche Scientifique, F-91198 Gif-sur-Yvette cedex, France
| | - Bogdan I. Iorga
- Institut de Chimie des Substances Naturelles, UPR 2301, Centre National de la Recherche Scientifique, F-91198 Gif-sur-Yvette cedex, France
| | - Carole Fruchart-Gaillard
- Service d'Ingénierie Moléculaire des Protéines, Laboratoire de Toxinologie Moléculaire et Biotechnologies, Commissariat à l'Energie Atomique, F-91191 Gif-sur-Yvette, France
| | - Evelyne Benoit
- Institut de Neurobiologie Alfred Fessard, FRC2118, Laboratoire de Neurobiologie et Développement, UPR-3294, Centre National de la Recherche Scientifique, F-91198 Gif-sur-Yvette cedex, France
| | - Zhenhua Gu
- Department of Chemistry and Biochemistry, University of California, Santa Barbara, California 93106-9510, United States
| | - Craig Stivala
- Department of Chemistry and Biochemistry, University of California, Santa Barbara, California 93106-9510, United States
| | - Armen Zakarian
- Department of Chemistry and Biochemistry, University of California, Santa Barbara, California 93106-9510, United States
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Ma Y, Hoepker AC, Gupta L, Faggin MF, Collum DB. 1,4-addition of lithium diisopropylamide to unsaturated esters: role of rate-limiting deaggregation, autocatalysis, lithium chloride catalysis, and other mixed aggregation effects. J Am Chem Soc 2010; 132:15610-23. [PMID: 20961095 PMCID: PMC2989387 DOI: 10.1021/ja105855v] [Citation(s) in RCA: 61] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
Abstract
Lithium diisopropylamide (LDA) in tetrahydrofuran at -78 °C undergoes 1,4-addition to an unsaturated ester via a rate-limiting deaggregation of LDA dimer followed by a post-rate-limiting reaction with the substrate. Muted autocatalysis is traced to a lithium enolate-mediated deaggregation of the LDA dimer and the intervention of LDA-lithium enolate mixed aggregates displaying higher reactivities than LDA. Striking accelerations are elicited by <1.0 mol % LiCl. Rate and mechanistic studies have revealed that the uncatalyzed and catalyzed pathways funnel through a common monosolvated-monomer-based intermediate. Four distinct classes of mixed aggregation effects are discussed.
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Affiliation(s)
- Yun Ma
- Department of Chemistry and Chemical Biology, Baker Laboratory, Cornell University, Ithaca, New York 14853-1301
| | - Alexander C. Hoepker
- Department of Chemistry and Chemical Biology, Baker Laboratory, Cornell University, Ithaca, New York 14853-1301
| | - Lekha Gupta
- Department of Chemistry and Chemical Biology, Baker Laboratory, Cornell University, Ithaca, New York 14853-1301
| | - Marc F. Faggin
- Department of Chemistry and Chemical Biology, Baker Laboratory, Cornell University, Ithaca, New York 14853-1301
| | - David B. Collum
- Department of Chemistry and Chemical Biology, Baker Laboratory, Cornell University, Ithaca, New York 14853-1301
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NMR studies of a ternary complex reagent of lithium ester enolate, chiral diether, and lithium diisopropylamide in an asymmetric Michael reaction. Tetrahedron 2010. [DOI: 10.1016/j.tet.2010.01.072] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
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21
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Lecachey B, Duguet N, Oulyadi H, Fressigné C, Harrison-Marchand A, Yamamoto Y, Tomioka K, Maddaluno J. Enantioselective Conjugate Addition of a Lithium Ester Enolate Catalyzed by Chiral Lithium Amides: A Possible Intermediate Characterized. Org Lett 2009; 11:1907-10. [DOI: 10.1021/ol900275y] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Baptiste Lecachey
- IRCOF, CNRS UMR 6014 & FR 3038, Université de Rouen, 76821 Mont St. Aignan Cedex, France, and Graduate School of Pharmaceutical Sciences, Kyoto University, Yoshida, Sakyo-ku, Kyoto 606-8501, Japan
| | - Nicolas Duguet
- IRCOF, CNRS UMR 6014 & FR 3038, Université de Rouen, 76821 Mont St. Aignan Cedex, France, and Graduate School of Pharmaceutical Sciences, Kyoto University, Yoshida, Sakyo-ku, Kyoto 606-8501, Japan
| | - Hassan Oulyadi
- IRCOF, CNRS UMR 6014 & FR 3038, Université de Rouen, 76821 Mont St. Aignan Cedex, France, and Graduate School of Pharmaceutical Sciences, Kyoto University, Yoshida, Sakyo-ku, Kyoto 606-8501, Japan
| | - Catherine Fressigné
- IRCOF, CNRS UMR 6014 & FR 3038, Université de Rouen, 76821 Mont St. Aignan Cedex, France, and Graduate School of Pharmaceutical Sciences, Kyoto University, Yoshida, Sakyo-ku, Kyoto 606-8501, Japan
| | - Anne Harrison-Marchand
- IRCOF, CNRS UMR 6014 & FR 3038, Université de Rouen, 76821 Mont St. Aignan Cedex, France, and Graduate School of Pharmaceutical Sciences, Kyoto University, Yoshida, Sakyo-ku, Kyoto 606-8501, Japan
| | - Yasutomo Yamamoto
- IRCOF, CNRS UMR 6014 & FR 3038, Université de Rouen, 76821 Mont St. Aignan Cedex, France, and Graduate School of Pharmaceutical Sciences, Kyoto University, Yoshida, Sakyo-ku, Kyoto 606-8501, Japan
| | - Kiyoshi Tomioka
- IRCOF, CNRS UMR 6014 & FR 3038, Université de Rouen, 76821 Mont St. Aignan Cedex, France, and Graduate School of Pharmaceutical Sciences, Kyoto University, Yoshida, Sakyo-ku, Kyoto 606-8501, Japan
| | - Jacques Maddaluno
- IRCOF, CNRS UMR 6014 & FR 3038, Université de Rouen, 76821 Mont St. Aignan Cedex, France, and Graduate School of Pharmaceutical Sciences, Kyoto University, Yoshida, Sakyo-ku, Kyoto 606-8501, Japan
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Alouane N, Bentayeb K, Vrancken E, Gérard H, Mangeney P. 1,3-Li/H Shift of 1-Aryl-1,2-alkadienyl Reagents: An Experimental and Theoretical Study. Chemistry 2009; 15:45-8. [DOI: 10.1002/chem.200801849] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
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23
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Riggs JC, Singh KJ, Yun M, Collum DB. Anionic Snieckus-Fries rearrangement: solvent effects and role of mixed aggregates. J Am Chem Soc 2008; 130:13709-17. [PMID: 18798619 PMCID: PMC2626637 DOI: 10.1021/ja804087r] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Lithiated aryl carbamates (ArLi) bearing methoxy or fluoro substituents in the meta position are generated from lithium diisopropylamide (LDA) in THF, n-BuOMe, Me2NEt, dimethoxyethane (DME), N,N,N',N'-tetramethylethylenediamine (TMEDA), N,N,N',N'-tetramethylcyclohexanediamine (TMCDA), and hexamethylphosphoramide (HMPA). The aryllithiums are shown with (6)Li, (13)C, and (15)N NMR spectroscopies to be monomers, ArLi-LDA mixed dimers, and ArLi-LDA mixed trimers, depending on the choice of solvent. Subsequent Snieckus-Fries rearrangements afford ArOLi-LDA mixed dimers and trimers of the resulting phenolates. Rate studies of the rearrangement implicate mechanisms based on monomers, mixed dimers, and mixed trimers.
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Affiliation(s)
- Jason C Riggs
- Department of Chemistry and Chemical Biology, Baker Laboratory, Cornell University, Ithaca, New York 14853-1301, USA
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24
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Godenschwager P, Collum DB. Lithium hexamethyldisilazide-mediated enolizations: influence of triethylamine on E/Z selectivities and enolate reactivities. J Am Chem Soc 2008; 130:8726-32. [PMID: 18557616 PMCID: PMC3021125 DOI: 10.1021/ja800250q] [Citation(s) in RCA: 60] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Lithium hexamethyldisilazide (LiHMDS) in triethylamine (Et 3N)/toluene is shown to enolize acyclic ketones and esters rapidly and with high E/ Z selectivity. Mechanistic studies reveal a dimer-based mechanism consistent with previous studies of LiHMDS/Et 3N. E/ Z equilibration occurs when <2.0 equiv of LiHMDS are used. Studies of the aldol condensation and Ireland-Claisen rearrangement of the resulting Et 3N-solvated enolates show higher and often complementary diastereoselectivities when compared with analogous reactions in THF. The Et 3N-solvated enolates also display a marked (20-fold) acceleration of the Ireland-Claisen rearrangement with evidence of autocatalysis. A possible importance of amine-solvated enolates is discussed.
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Affiliation(s)
- Peter Godenschwager
- Contribution from the Department of Chemistry and Chemical Biology Baker Laboratory, Cornell University Ithaca, New York 14853-1301
| | - David B. Collum
- Contribution from the Department of Chemistry and Chemical Biology Baker Laboratory, Cornell University Ithaca, New York 14853-1301
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25
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He X, Hurley E, Noll BC, Henderson KW. Regio- and Stereoselective Enolizations Using Calcium Bis(hexamethyldisilazide) as a Base: Synthetic, Solid-State, and Solution Studies. Organometallics 2008. [DOI: 10.1021/om7011908] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Xuyang He
- Department of Chemistry and Biochemistry, University of Notre Dame, Notre Dame, Indiana 46556-5670
| | - Erin Hurley
- Department of Chemistry and Biochemistry, University of Notre Dame, Notre Dame, Indiana 46556-5670
| | - Bruce C. Noll
- Department of Chemistry and Biochemistry, University of Notre Dame, Notre Dame, Indiana 46556-5670
| | - Kenneth W. Henderson
- Department of Chemistry and Biochemistry, University of Notre Dame, Notre Dame, Indiana 46556-5670
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26
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Liu J, Li D, Sun C, Williard PG. Analysis of an asymmetric addition with a 2:1 mixed lithium amide/n-butyllithium aggregate. J Org Chem 2008; 73:4045-52. [PMID: 18459811 DOI: 10.1021/jo800592d] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
A 2:1 lithium amide/ n-butyllithium aggregate 1 is investigated as an asymmetric addition template in hydrocarbon solvents. Several different chiral lithium amides were synthesized from l-valine and tested in the asymmetric addition of n-BuLi to various aldehydes. Enantiomeric excesses up to 83% were obtained in the case of the addition of n-BuLi to pivaldehyde at -116 degrees C in pentane. (1)H and (13)C INEPT DOSY were utilized to characterize a new trimeric complex 12 between 2 equiv of lithium amide and 1 equiv of lithium alkoxide. This mixed aggregate strongly indicates the possibility of product-induced chirality inhibition that is detrimental to the enantioselectivity of asymmetric addition reaction.
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Affiliation(s)
- Jia Liu
- Department of Chemistry, Brown University, Providence, RI 02912, USA
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27
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Yu H, Richey RN, Stout JR, LaPack MA, Gu R, Khau VV, Frank SA, Ott JP, Miller RD, Carr MA, Zhang TY. Development of a Practical Synthesis of DPP IV Inhibitor LY2497282. Org Process Res Dev 2008. [DOI: 10.1021/op700235c] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Hannah Yu
- Chemical Product Research and Development, Lilly Research Laboratories,
Eli Lilly and Company, Indianapolis, Indiana, 46285-4813, U.S.A
| | - Rachel N. Richey
- Chemical Product Research and Development, Lilly Research Laboratories,
Eli Lilly and Company, Indianapolis, Indiana, 46285-4813, U.S.A
| | - James R. Stout
- Chemical Product Research and Development, Lilly Research Laboratories,
Eli Lilly and Company, Indianapolis, Indiana, 46285-4813, U.S.A
| | - Mark A. LaPack
- Chemical Product Research and Development, Lilly Research Laboratories,
Eli Lilly and Company, Indianapolis, Indiana, 46285-4813, U.S.A
| | - Ruilin Gu
- Chemical Product Research and Development, Lilly Research Laboratories,
Eli Lilly and Company, Indianapolis, Indiana, 46285-4813, U.S.A
| | - Vien V. Khau
- Chemical Product Research and Development, Lilly Research Laboratories,
Eli Lilly and Company, Indianapolis, Indiana, 46285-4813, U.S.A
| | - Scott A. Frank
- Chemical Product Research and Development, Lilly Research Laboratories,
Eli Lilly and Company, Indianapolis, Indiana, 46285-4813, U.S.A
| | - Joel P. Ott
- Chemical Product Research and Development, Lilly Research Laboratories,
Eli Lilly and Company, Indianapolis, Indiana, 46285-4813, U.S.A
| | - Richard D. Miller
- Chemical Product Research and Development, Lilly Research Laboratories,
Eli Lilly and Company, Indianapolis, Indiana, 46285-4813, U.S.A
| | - Michael A. Carr
- Chemical Product Research and Development, Lilly Research Laboratories,
Eli Lilly and Company, Indianapolis, Indiana, 46285-4813, U.S.A
| | - Tony Y. Zhang
- Chemical Product Research and Development, Lilly Research Laboratories,
Eli Lilly and Company, Indianapolis, Indiana, 46285-4813, U.S.A
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28
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Ma Y, Collum DB. Lithium diisopropylamide-mediated reactions of imines, unsaturated esters, epoxides, and aryl carbamates: influence of hexamethylphosphoramide and ethereal cosolvents on reaction mechanisms. J Am Chem Soc 2007; 129:14818-25. [PMID: 17985891 DOI: 10.1021/ja074554e] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Several reactions mediated by lithium diisopropylamide (LDA) with added hexamethylphosphoramide (HMPA) are described. The N-isopropylimine of cyclohexanone lithiates via an ensemble of monomer-based pathways. Conjugate addition of LDA/HMPA to an unsaturated ester proceeds via di- and tetra-HMPA-solvated dimers. Deprotonation of norbornene epoxide by LDA/HMPA proceeds via an intermediate metalated epoxide as a mixed dimer with LDA. Ortholithiation of an aryl carbamate proceeds via a mono-HMPA-solvated monomer-based pathway. Dependencies on THF and other ethereal cosolvents suggest that secondary-shell solvation effects are important in some instances. The origins of the inordinate mechanistic complexity are discussed.
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Affiliation(s)
- Yun Ma
- Department of Chemistry and Chemical Biology, Baker Laboratory, Cornell University, Ithaca, New York 14853-1301, USA
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29
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Godenschwager PF, Collum DB. Lithium Hexamethyldisilazide-Mediated Enolizations: Influence of Chelating Ligands and Hydrocarbon Cosolvents on the Rates and Mechanisms. J Am Chem Soc 2007; 129:12023-31. [PMID: 17850084 DOI: 10.1021/ja074018m] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Enolizations of 2-methylcyclohexanone by lithium hexamethyldisilazide (LiHMDS) in the presence of three chelating ligands--trans-N,N,N',N'-tetramethylcyclohexanediamine, N,N,N',N'-tetramethylethylenediamine, and dimethoxyethane--reveal an approximate 40-fold range of rates. NMR spectroscopic analyses and rate studies reveal isostructural transition structures based on monomeric LiHMDS for the diamines. Rate studies of LiHMDS/dimethoxyethane-mediated enolizations implicate a substantial number of monomer- and dimer-based mechanisms. The rate laws vary for the three ligands because of ligand-dependent structural differences in both the reactants and the transition structures. The importance of LiHMDS-ketone complexes and the role of hydrocarbon cosolvents are discussed.
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Affiliation(s)
- Peter F Godenschwager
- Department of Chemistry and Chemical Biology, Baker Laboratory, Cornell University Ithaca, New York 14853-1301, USA
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30
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Collum DB, McNeil AJ, Ramirez A. Lithium diisopropylamide: solution kinetics and implications for organic synthesis. Angew Chem Int Ed Engl 2007; 46:3002-17. [PMID: 17387670 DOI: 10.1002/anie.200603038] [Citation(s) in RCA: 169] [Impact Index Per Article: 9.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Lithium diisopropylamide (LDA) is a prominent reagent used in organic synthesis. In this Review, rate studies of LDA-mediated reactions are placed in the broader context of organic synthesis in three distinct segments. The first section provides a tutorial on solution kinetics, emphasizing the characteristic rate behavior caused by dominant solvation and aggregation effects. The second section summarizes substrate- and solvent-dependent mechanisms that reveal basic principles of solvation and aggregation. The final section suggests how an understanding of mechanism might be combined with empirical methods to optimize yields, rates, and selectivities of organolithium reactions and applied to organic synthesis.
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Affiliation(s)
- David B Collum
- Department of Chemistry and Chemical Biology, Baker Laboratory, Cornell University, Ithaca, NY 14853-1301, USA.
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31
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Collum D, McNeil A, Ramirez A. Lithiumdiisopropylamid: Reaktionskinetik in Lösung und Folgerungen für die organische Synthese. Angew Chem Int Ed Engl 2007. [DOI: 10.1002/ange.200603038] [Citation(s) in RCA: 53] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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32
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Ma Y, Ramirez A, Singh KJ, Keresztes I, Collum DB. Lithium Diisopropylamide Solvated by Hexamethylphosphoramide: Substrate-Dependent Mechanisms for Dehydrobrominations. J Am Chem Soc 2006; 128:15399-404. [PMID: 17132006 DOI: 10.1021/ja060964b] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Lithium diisopropylamide-mediated dehydrobrominations of exo-2-bromonorbornane, 1-bromocyclooctene, and cis-4-bromo-tert-butylcyclohexane were studied in THF solutions and THF solutions with added hexamethylphosphoramide (HMPA). Rate studies reveal a diverse array of mechanisms based on mono-, di-, and trisolvated monomers as well as triple ions. The results are contrasted with analogous eliminations in THF in the absence of HMPA.
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Affiliation(s)
- Yun Ma
- Department of Chemistry and Chemical Biology, Baker Laboratory, Cornell University, Ithaca, New York 14853-1301, USA
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33
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Green JR, Majewski M, Snieckus V. Deprotonation of β,β-disubstituted α,β-unsaturated amides - Mechanism and stereochemical consequences. CAN J CHEM 2006. [DOI: 10.1139/v06-112] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
A detailed study of the lithium dialkylamide induced deprotonation of β,β-disubstituted α,β-unsaturated amides is presented. The preferential γ-Z-deprotonation and stereochemical outcome of substituents on the γ-Z carbon atom are rationalized in terms of a cyclic eight-membered transition state, which is supported by DFT calculations. Analogous deprotonations on cyclohexylidenecarboxamides reveal a delicate balance of the preference for the eight-membered cyclic transition state with the effects of existing substituents on the ring and the intervention of a twist-boat transition state.Key words: dienolate, amide, deprotonation mechanism, transition state, enolization, regioselectivity, stereoselectivity.
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34
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Singh KJ, Collum DB. Lithium Diisopropylamide-Mediated Ortholithiation and Anionic Fries Rearrangement of Aryl Carbamates: Role of Aggregates and Mixed Aggregates. J Am Chem Soc 2006; 128:13753-60. [PMID: 17044703 DOI: 10.1021/ja064655x] [Citation(s) in RCA: 65] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Structural and mechanistic studies of the lithium diisopropylamide (LDA)-mediated anionic Fries rearrangements of aryl carbamates are described. Substituents at the meta position of the arene (H, OMe, F) and the dialkylamino moiety of the carbamate (Me(2)N, Et(2)N, and i-Pr(2)N) markedly influence the relative rates of ortholithiation and subsequent Fries rearrangement. Structural studies using (6)Li and (15)N NMR spectroscopies on samples derived from [(6)Li,(15)N]LDA reveal an LDA dimer, LDA dimer-arene complexes, an aryllithium monomer, LDA-aryllithium mixed dimers, an LDA-lithium phenolate mixed dimer, and homoaggregated lithium phenolates. The highly insoluble phenolate was characterized as a dimer by X-ray crystallography. Rate studies show monomer- and dimer-based ortholithiations as well as monomer- and mixed dimer-based Fries rearrangements. Density functional theory computational studies probe experimentally elusive structural and mechanistic details.
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Affiliation(s)
- Kanwal Jit Singh
- Department of Chemistry and Chemical Biology, Baker Laboratory, Cornell University, Ithaca, New York 14853-1301, USA
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35
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Ramirez A, Sun X, Collum DB. Lithium Diisopropylamide-Mediated Enolization: Catalysis by Hemilabile Ligands. J Am Chem Soc 2006; 128:10326-36. [PMID: 16881665 DOI: 10.1021/ja062147h] [Citation(s) in RCA: 65] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Structural, kinetic, and computational studies reveal the mechanistic complexities of a lithium diisopropylamide (LDA)-mediated ester enolization. Hemilabile amino ether MeOCH2CH2NMe2, binding as an eta1 (ether-bound) ligand in the reactant and as an eta2 (chelating) ligand in the transition structure, accelerates the enolization 10,000-fold compared with n-BuOMe. At the onset of the reaction, a dimer-based enolization prevails. As the reaction proceeds, significantly less reactive LDA-enolate mixed dimers appear and divert the reaction through monomer- and mixed dimer-based pathways. The mechanistic and computational investigations lead to a proof-of-principle ligand-catalyzed enolization in which an ancillary ligand allows the catalytic ligand to re-enter the catalytic cycle.
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Affiliation(s)
- Antonio Ramirez
- Department of Chemistry and Chemical Biology, Baker Laboratory, Cornell University, Ithaca, New York 14853-1301, USA
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36
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Ohta Y, Demura A, Okamoto T, Hitomi H, Nagaoka M. The Body-Centered Cubic Structure of Methyllithium Tetramer Crystal: Staggered Methyl Conformation by Electrostatic Stabilization via Intratetramer Multipolarization. J Phys Chem B 2006; 110:12640-4. [PMID: 16800596 DOI: 10.1021/jp057014h] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The methyllithium tetramer (CH3Li)4 structure in the bcc crystal has been theoretically optimized with the use of density functional theory calculations under the periodic boundary condition. The X-ray structure shows that the methyl-group conformation in tetramer in crystal takes the staggered form rather than the eclipsed form that is taken in the isolated tetramer, i.e., the crystal packing effect, and this has been reproduced for the first time. It is concluded that the staggered form is advantageous in crystal, as a whole, due to the larger electrostatic stabilization via the induced intratetramer multipolarization, although it should cause, simultaneously, smaller destabilization in intratetramer electronic energy.
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Affiliation(s)
- Yusuke Ohta
- Graduate School of Information Science, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8601, Japan
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37
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Solvent and Ligand Effects on the Tandem Addition-Lithiation-Electrophilic Substitution of Phenyllithium on α,β-Unsaturated Carbonyl Compounds. Int J Mol Sci 2005. [DOI: 10.3390/i6010097] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022] Open
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38
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Ordóñez M, Hernández-Fernández E, Xahuentitla J, Cativiela C. Asymmetric alkylation of dimethoxyphosphoryl-N-[1-(S)-alpha-methylbenzyl]acetamide enolates. Synthesis of both stereoisomers from the same source of chirality by changing the equivalents of LDA. Chem Commun (Camb) 2005:1336-8. [PMID: 15742070 DOI: 10.1039/b416616g] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
A new methodology has been developed for the synthesis of both stereoisomers from a single chiral source.
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Affiliation(s)
- Mario Ordóñez
- Centro de Investigaciones Químicas, Universidad Autónoma del Estado de Morelos, Av. Universidad 1001, 62210 Cuernavaca, Mor., Mexico.
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39
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Abstract
Palladium-catalyzed asymmetric allylic alkylation of nonstabilized ketone enolates to generate quaternary centers has been achieved in excellent yield and enantioselectivity. Optimized conditions consist of performing the reaction in the presence of two equivalents of LDA as base, one equivalent of trimethytin chloride as a Lewis acid, 1,2-dimethoxyethane as the solvent, and a catalytic amount of a chiral palladium complex formed from pi-allyl palladium chloride dimer 3 and cyclohexyldiamine derived chiral ligand 4. Linearly substituted, acyclic 1,3-dialkyl substituted, and unsubstituted allylic carbonates function well as electrophiles. A variety of alpha-tetralones, cyclohexanones, and cyclopentanones can be employed as nucleophiles. The absolute configuration generated is consistent with the current model in which steric factors control stereofacial differentiation. The quaternary substituted products available by this method are versatile substrates for further elaboration.
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Affiliation(s)
- Barry M Trost
- Department of Chemistry, Stanford University, Stanford, CA 94305-5080, USA.
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40
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Davlieva MG, Lü JM, Lindeman SV, Kochi JK. Crystallographic Distinction between “Contact” and “Separated” Ion Pairs: Structural Effects on Electronic/ESR Spectra of Alkali-Metal Nitrobenzenides. J Am Chem Soc 2004; 126:4557-65. [PMID: 15070374 DOI: 10.1021/ja049856k] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The classic nitrobenzene anion-radical (NB(-*) or nitrobenzenide) is isolated for the first time as pure crystalline alkali-metal salts. The deliberate use of the supporting ligands 18-crown-6 and [2.2.2]cryptand allows the selective formation of contact ion pairs designated as (crown)M(+)NB(-*), where M(+) = K(+), Rb(+), and Cs(+), as well as the separated ion pair K(cryptand)(+)NB(-*)-both series of which are structurally characterized by precise low-temperature X-ray crystallography, ESR analysis, and UV-vis spectroscopy. The unusually delocalized structure of NB(-*) in the separated ion pair follows from the drastically shortened N-C bond and marked quinonoidal distortion of the benzenoid ring to signify complete (95%) electronic conjugation with the nitro substituent. On the other hand, the formation of contact ion pairs results in the substantial decrease of electronic conjugation in inverse order with cation size (K(+) > Rb(+)) owing to increased localization of negative charge from partial (NO(2)) bonding to the alkali-metal cation. Such a loss in electronic conjugation (or reverse charge transfer) may be counterintuitive, but it is in agreement with the distribution of odd-electron spin electron density from the ESR data and with the hypsochromic shift of the characteristic absorption band in the electronic spectra. Most importantly, this crystallographic study underscores the importance of ion-pair structure on the intrinsic property (and thus reactivity) of the component ions-as focused here on the nitrobenzenide anion.
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Affiliation(s)
- Milya G Davlieva
- Department of Chemistry, University of Houston, Houston, Texas 77204-5003, USA
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41
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Zhao P, Lucht BL, Kenkre SL, Collum DB. Lithium Hexamethyldisilazide-Mediated Ketone Enolization: The Influence of Hindered Dialkyl Ethers and Isostructural Dialkylamines on Reaction Rates and Mechanisms. J Org Chem 2003; 69:242-9. [PMID: 14725435 DOI: 10.1021/jo030221y] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Mechanistic studies of the enolization of 2-methylcyclohexanone mediated by lithium hexamethyldisilazide (LiHMDS; TMS(2)NLi) solvated by hindered dialkyl ethers (ROR') are described. Rate studies using in situ IR spectroscopy show that enolizations in the presence of i-Pr(2)O, 2,2,5,5-tetramethyltetrahydrofuran, and cineole proceed via dimer-based transition structures [(TMS(2)NLi)(2)(ROR')(ketone)]. Comparing the relative solvation energies and the corresponding solvent-dependent activation energies shows that the highly substituted ethers accelerate the enolizations by sterically destabilizing the reactants and stabilizing the transition structures. Comparisons of hindered dialkyl ethers with their isostructural dialkylamines reveal that the considerably higher rates elicited by the amines derive from an analogous relative destabilization of the reactants and relative stabilization of the transition structures.
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Affiliation(s)
- Pinjing Zhao
- Department of Chemistry and Chemical Biology, Baker Laboratory, Cornell University, Ithaca, New York 14853-1301, USA
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42
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Pratt LM, Mogali S, Glinton K. Solvent effects on the aggregation state of lithium dialkylaminoborohydrides. J Org Chem 2003; 68:6484-8. [PMID: 12919007 DOI: 10.1021/jo034498+] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
DFT calculations were performed to determine the effects of ethereal solvents on the aggregation state of lithium dialkylaminoborohydrides (LABs). The calculations included dimerization energies in the gas phase, with continuum solvation only, microsolvation with coordinating ethereal ligands, and a combination of the microsolvation and continuum models. The continuum model alone overestimates the stability of the dimers, apparently due to the lack of steric effects from the coordinating ethereal ligands. The use of the combined microsolvation and continuum solvation models predicts lithium dimethylaminoborohydride to be a mixture of monomer and dimer in THF, and more sterically hindered lithium aminoborohydrides to exist primarily as monomers. The kinetics of amination of 1-chlorodecane by lithium dimethylaminoborohydride showed no detectable change in reaction rate with time, suggesting that the LAB reagent may exist primarily as a monomer in THF.
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Affiliation(s)
- Lawrence M Pratt
- Department of Chemistry, Fisk University, 1000 17th Avenue North, Nashville, Tennessee 37208, USA.
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43
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Zhao P, Collum DB. Lithium hexamethyldisilazide/triethylamine-mediated ketone enolization: remarkable rate accelerations stemming from a dimer-based mechanism. J Am Chem Soc 2003; 125:4008-9. [PMID: 12670196 DOI: 10.1021/ja021284l] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Mechanistic studies of the enolization of 2-methylcyclohexanone mediated by lithium hexamethyldisilazide (LiHMDS; TMS2NLi) in toluene and toluene/triethylamine (Et3N) mixtures are described. Structural studies of LiHMDS/ketone mixtures in toluene reveal cyclic dimer (TMS2NLi)2(ketone). Rate studies using in situ IR spectroscopy show the enolization proceeds via a dimer-based transition structure, [(TMS2NLi)2(ketone)]. NMR spectroscopic studies of LiHMDS/ketone mixtures in the presence of relatively unhindered trialkylamines such as Me2NEt reveal the quantitative formation of cyclic dimers of general structure (TMS2NLi)2(Et3N)(ketone). Rate studies trace a >3000-fold rate acceleration to a dimer-based transition structure, [(TMS2NLi)2(Et3N)(ketone)].
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Affiliation(s)
- Pinjing Zhao
- Department of Chemistry and Chemical Biology, Baker Laboratory, Cornell University, Ithaca, New York 14853-1301, USA
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44
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Brandt P, Haeffner F. A DFT-derived model predicts solvation-dependent configurational stability of organolithium compounds: a case study of a chiral alpha-thioallyllithium compound. J Am Chem Soc 2003; 125:48-9. [PMID: 12515505 DOI: 10.1021/ja0279491] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Density functional theory calculations (B3LYP/6-31+G*) were performed to evaluate a model previously published by us which suggests that aggregation and solvation of organolithium compounds can be of large importance for their configurational stability. In this study, we demonstrate how THF solvation of the monomer of a chiral alpha-thioallyllithium compound impedes the racemization, while upon dimerization the inversion process accelerates. These findings agree with experiments performed by Hoppe and co-workers. These findings may be used to further develop organolithium compounds which should be designed to resist aggregation and efficient transition-state solvation.
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Affiliation(s)
- Peter Brandt
- Department of Structural Chemistry, Biovitrum AB, 112 76 Stockholm, Sweden
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45
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Pratt LM, Ramachandran B, Xidos JD, Cramer CJ, Truhlar DG. Structures and aggregation states of fluoromethyllithium and chloromethyllithium carbenoids in the gas phase and in ethereal solvent. J Org Chem 2002; 67:7607-12. [PMID: 12398479 DOI: 10.1021/jo026022g] [Citation(s) in RCA: 40] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Using high-level quantum mechanical calculations and various models to account for solvation effects, monomers and dimers of fluoromethyllithium and chloromethyllithium carbenoids are studied in the gas phase and in dimethyl ether solvent. A combination of explicit microsolvation and a continuum reaction field is required to account fully for the structural and energetic effects of solvation. One important effect of solvent is the stabilization of charge-separated structures in which the lithium-halogen distance is much greater than in the gas-phase structures. At the most complete level of theory the 173 K standard-state free energy of dimerization of fluoromethyllithium in dimethyl ether is predicted to be -0.9 kcal mol(-)(1), while that for chloromethyllithium in the same solvent is predicted to be 3.7 kcal mol(-)(1). This suggests that, under typical experimental conditions, dimers of chloroalkyllithiums will not be observed, while dimers of fluoroalkyllithiums may contribute to the equilibrium population at a detectable level.
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Affiliation(s)
- Lawrence M Pratt
- Department of Chemistry and Supercomputer Institute, University of Minnesota, 207 Pleasant St. S.E., Minneapolis 55455-0431, USA.
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Fort Y, Gros P, Rodriguez AL. First one-pot chemo-, regio- and enantioselective functionalisation of pyridine compounds mediated by BuLi-(S)-(−)-N-methyl-2-pyrrolidine methoxide. ACTA ACUST UNITED AC 2001. [DOI: 10.1016/s0957-4166(01)00454-2] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
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