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Yang X, Fleming FF. C- and N-Metalated Nitriles: The Relationship between Structure and Selectivity. Acc Chem Res 2017; 50:2556-2568. [PMID: 28930437 DOI: 10.1021/acs.accounts.7b00329] [Citation(s) in RCA: 37] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
Metalated nitriles are exceptional nucleophiles capable of forging highly hindered stereocenters in cases where enolates are unreactive. The excellent nucleophilicity emanates from the powerful inductive stabilization of adjacent negative charge by the nitrile, which has a miniscule steric demand. Inductive stabilization is the key to understanding the reactivity of metalated nitriles because this permits a continuum of structures that range from N-metalated ketenimines to nitrile anions. Solution and solid-state analyses reveal two different metal coordination sites, the formally anionic carbon and the nitrile nitrogen, with the site of metalation depending intimately on the solvent, counterion, temperature, and ligands. The most commonly encountered structures, C- and N-metalated nitriles, have either sp3 or sp2 hybridization at the nucleophilic carbon, which essentially translates into two distinct organometallic species with similar but nonidentical stereoselectivity, regioselectivity, and reactivity preferences. The hybridization differences are particularly important in SNi displacements of cyclic nitriles because the orbital orientations create very precise trajectories that control the cyclization selectivity. Harnessing the orbital differences between C- and N-metalated nitriles allows selective cyclization to afford nitrile-containing cis- or trans-hydrindanes, decalins, or bicyclo[5.4.0]undecanes. Similar orbital constraints favor preferential SNi displacements with allylic electrophiles on sp3 centers over sp2 centers. The strategy permits stereoselective displacements on secondary centers to set contiguous tertiary and quaternary stereocenters or even contiguous vicinal quaternary centers. Stereoselective alkylations of acyclic nitriles are inherently more challenging because of the difficulty in creating steric differentiation in a dynamic system with rotatable bonds. However, judicious substituent placement of vicinal dimethyl groups and a trisubstituted alkene sufficiently constrains C- and N-metalated nitriles to install quaternary stereocenters with excellent 1,2-induction. The structural differences between C- and N-metalated nitriles permit a rare series of chemoselective alkylations with bifunctional electrophiles. C-Magnesiated nitriles preferentially react with carbonyl electrophiles, whereas N-lithiated nitriles favor SN2 displacement of alkyl halides. The chemoselective alkylations potentially provide a strategy for late-stage alkylations of polyfunctional electrophiles en route to bioactive targets. In this Account, the bonding of metalated nitriles is summarized as a prelude to the different strategies for selectively preparing C- and N-metalated nitriles. With this background, the Account then transitions to applications in which C- or N-metalated nitriles allow complementary diastereoselectivity in alkylations and arylations, and regioselective alkylations and arylations, with acyclic and cyclic nitriles. In the latter sections, a series of regiodivergent cyclizations are described that provide access to cis- and trans-hydrindanes and decalins, structural motifs embedded within a plethora of natural products. The last section describes chemoselective alkylations and acylations of C- and N-metalated nitriles that offer the tantalizing possibility of selectively manipulating functional groups in bioactive medicinal leads without recourse to protecting groups. Collectively, the unusual reactivity profiles of C- and N-metalated nitriles provide new strategies for rapidly and selectively accessing valuable synthetic precursors.
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Affiliation(s)
- Xun Yang
- Department of Chemistry, Drexel University, Philadelphia, Pennsylvania 19104, United States
| | - Fraser F. Fleming
- Department of Chemistry, Drexel University, Philadelphia, Pennsylvania 19104, United States
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Kotomori Y, Sasaki M, Kawahata M, Yamaguchi K, Takeda K. Stereochemical Course of Deprotonation-Acylation of N-Boc- and N-Carbamoyl-2-cyano-6-methylpiperidines. J Org Chem 2015; 80:11013-20. [PMID: 26457453 DOI: 10.1021/acs.joc.5b02178] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The stereochemical course of electrophilic substitution of α-nitrile metallocarbanions generated by deprotonation from N-Boc- and N-carbamoyl-2-cyano-6-methylpiperidines was investigated. Deprotonation in the presence of an electrophile taking advantage of the high acidity of α-nitrile protons allowed examination of the effects of a chelating group on the nitrogen atom, a countercation, and the reactivity of an electrophile on the steric course. Analyses of reactions using aroyl chlorides and methyl iodide revealed the following: (1) the substitution reactions basically proceed with retention of configuration, (2) the extent of an inversion product increases with decreasing chelating ability of the N-substituent and with increasing leaving ability (ionic character) of a countercation (Li, Na, K) of the anionic species, and (3) the use of a more reactive electrophile results in an increase of the retention product.
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Affiliation(s)
- Yuri Kotomori
- Department of Synthetic Organic Chemistry, Institute of Biomedical & Health Sciences, Hiroshima University , 1-2-3 Kasumi, Minami-Ku, Hiroshima 734-8553, Japan
| | - Michiko Sasaki
- Department of Synthetic Organic Chemistry, Institute of Biomedical & Health Sciences, Hiroshima University , 1-2-3 Kasumi, Minami-Ku, Hiroshima 734-8553, Japan
| | - Masatoshi Kawahata
- Pharmaceutical Sciences at Kagawa Campus, Tokushima Bunri University , 1314-1 Shido, Sanuki, Kagawa 769-2193, Japan
| | - Kentaro Yamaguchi
- Pharmaceutical Sciences at Kagawa Campus, Tokushima Bunri University , 1314-1 Shido, Sanuki, Kagawa 769-2193, Japan
| | - Kei Takeda
- Department of Synthetic Organic Chemistry, Institute of Biomedical & Health Sciences, Hiroshima University , 1-2-3 Kasumi, Minami-Ku, Hiroshima 734-8553, Japan
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Ando M, Sasaki M, Miyashita I, Takeda K. Formation of 2-Cyano-2-siloxyvinylallenes via Cyanide-Induced Brook Rearrangement in γ-Bromo-α,β,γ,δ-unsaturated Acylsilanes. J Org Chem 2014; 80:247-55. [DOI: 10.1021/jo502323v] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Affiliation(s)
- Masafumi Ando
- Department of Synthetic Organic Chemistry, Institute of Biomedical & Health Sciences, Hiroshima University, 1-2-3 Kasumi, Minami-Ku, Hiroshima 734-8553, Japan
| | - Michiko Sasaki
- Department of Synthetic Organic Chemistry, Institute of Biomedical & Health Sciences, Hiroshima University, 1-2-3 Kasumi, Minami-Ku, Hiroshima 734-8553, Japan
| | - Izumi Miyashita
- Department of Synthetic Organic Chemistry, Institute of Biomedical & Health Sciences, Hiroshima University, 1-2-3 Kasumi, Minami-Ku, Hiroshima 734-8553, Japan
| | - Kei Takeda
- Department of Synthetic Organic Chemistry, Institute of Biomedical & Health Sciences, Hiroshima University, 1-2-3 Kasumi, Minami-Ku, Hiroshima 734-8553, Japan
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Sasaki M, Takegawa T, Sakamoto K, Kotomori Y, Otani Y, Ohwada T, Kawahata M, Yamaguchi K, Takeda K. Enantiodivergent Deprotonation/Acylation of α-Amino Nitriles. Angew Chem Int Ed Engl 2013; 52:12956-60. [DOI: 10.1002/anie.201306443] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/24/2013] [Revised: 09/03/2013] [Indexed: 11/06/2022]
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5
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Sasaki M, Takegawa T, Sakamoto K, Kotomori Y, Otani Y, Ohwada T, Kawahata M, Yamaguchi K, Takeda K. Enantiodivergent Deprotonation/Acylation of α-Amino Nitriles. Angew Chem Int Ed Engl 2013. [DOI: 10.1002/ange.201306443] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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Gao M, Patwardhan NN, Carlier PR. Stereochemical Inversion of a Cyano-Stabilized Grignard Reagent: Remarkable Effects of the Ethereal Solvent Structure and Concentration. J Am Chem Soc 2013; 135:14390-400. [DOI: 10.1021/ja407348s] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Ming Gao
- Department of Chemistry, Virginia Tech, Blacksburg, Virginia 24061, United States
| | - Neeraj N. Patwardhan
- Department of Chemistry, Virginia Tech, Blacksburg, Virginia 24061, United States
| | - Paul R. Carlier
- Department of Chemistry, Virginia Tech, Blacksburg, Virginia 24061, United States
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Chirality transfer in Brook rearrangement-mediated SE2′ solvolytic protonation and its use in estimation of the propensity for racemization of the α-lithiocarbanions of the substituents. Tetrahedron 2013. [DOI: 10.1016/j.tet.2013.05.043] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
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Affiliation(s)
| | - Kei Takeda
- Institute of Biomedical & Health Sciences, Hiroshima University
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Nath D, Fleming FF. Sulfinylnitriles: Sulfinyl-Metal Exchange-Alkylation Strategies. Chemistry 2012; 19:2023-9. [DOI: 10.1002/chem.201203174] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/06/2012] [Indexed: 11/09/2022]
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Mycka RJ, Duez S, Bernhardt S, Heppekausen J, Knochel P, Fleming FF. Cyclohexylcarbonitriles: Diastereoselective Arylations with TMPZnCl·LiCl. J Org Chem 2012; 77:7671-6. [DOI: 10.1021/jo301127n] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Robert J. Mycka
- Department of Chemistry and
Biochemistry, Duquesne University, Pittsburgh,
Pennsylvania 15282-1530, United States
| | - Stéphanie Duez
- Department Chemie, Ludwig-Maximilians-Universität, Butenandtstrasse
5-13, 81377, München, Germany
| | - Sebastian Bernhardt
- Department Chemie, Ludwig-Maximilians-Universität, Butenandtstrasse
5-13, 81377, München, Germany
| | - Johannes Heppekausen
- Department Chemie, Ludwig-Maximilians-Universität, Butenandtstrasse
5-13, 81377, München, Germany
| | - Paul Knochel
- Department Chemie, Ludwig-Maximilians-Universität, Butenandtstrasse
5-13, 81377, München, Germany
| | - Fraser F. Fleming
- Department of Chemistry and
Biochemistry, Duquesne University, Pittsburgh,
Pennsylvania 15282-1530, United States
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Sasaki M, Takegawa T, Ikemoto H, Kawahata M, Yamaguchi K, Takeda K. Enantioselective trapping of an α-chiral carbanion of acyclic nitrile by a carbon electrophile. Chem Commun (Camb) 2012; 48:2897-9. [PMID: 22314962 DOI: 10.1039/c2cc00082b] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Affiliation(s)
- Michiko Sasaki
- Department of Synthetic Organic Chemistry, Graduate School of Biomedical Sciences, Hiroshima University, 1-2-3 Kasumi, Minami-Ku, Hiroshima, 734-8553, Japan
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Nath D, Fleming FF. Nitrile Alkylations through Sulfinyl-Metal Exchange. Angew Chem Int Ed Engl 2011; 50:11790-3. [DOI: 10.1002/anie.201105630] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/08/2011] [Revised: 10/12/2011] [Indexed: 11/11/2022]
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Patwardhan NN, Gao M, Carlier PR. Incremental Solvation Precedes Ion-Pair Separation in Enantiomerization of a Cyano-Stabilized Grignard Reagent. Chemistry 2011; 17:12250-3. [DOI: 10.1002/chem.201102253] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/21/2011] [Indexed: 11/11/2022]
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Capriati V, Florio S, Perna F, Salomone A. Lithiated Fluorinated Styrene Oxides: Configurational Stability, Synthetic Applications, and Mechanistic Insight. Chemistry 2010; 16:9778-88. [DOI: 10.1002/chem.201000897] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
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16
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Deora N, Carlier PR. Computational Studies of Ion-Pair Separation of Benzylic Organolithium Compounds in THF: Importance of Explicit and Implicit Solvation. J Org Chem 2010; 75:1061-9. [DOI: 10.1021/jo9016452] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
Affiliation(s)
- Nipa Deora
- Department of Chemistry, Virginia Tech, Blacksburg, Virginia 24060
| | - Paul R. Carlier
- Department of Chemistry, Virginia Tech, Blacksburg, Virginia 24060
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Sasaki M, Ikemoto H, Kawahata M, Yamaguchi K, Takeda K. [2,3]-Wittig Rearrangement of Enantiomerically Enriched 3-Substituted 1-Propenyloxy-1-phenyl-2-propen-1-yl Carbanions: Effect of Heteroatoms and Conjugating Groups on Planarization of an α-Oxy-Benzylcarbanion through a Double Bond. Chemistry 2009; 15:4663-6. [DOI: 10.1002/chem.200802322] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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Sasaki M, Shirakawa Y, Kawahata M, Yamaguchi K, Takeda K. Stereoselective SE2′ Protonation of α-Hydroxyallylsilanes Mediated by a Brook Rearrangement. Chemistry 2009; 15:3363-6. [DOI: 10.1002/chem.200802499] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
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Fleming FF, Gudipati S. Cyclic Metalated Nitriles: Stereoselective Cyclizations to cis- and trans-Hydrindanes, Decalins, and Bicyclo[4.3.0]undecanes. European J Org Chem 2008; 2008:10.1002/ejoc.200800715. [PMID: 24260015 PMCID: PMC3831376 DOI: 10.1002/ejoc.200800715] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/18/2008] [Indexed: 11/07/2022]
Abstract
Metalated nitriles are nucleophilic chameleons whose precise identity is determined by the nature of the metal, the solvent, the temperature, and the structure of the nitrile. The review surveys the different structural types and their cyclization trajectories to show how to selectively tune the metalated nitrile geometry for stereoselective cyclizations to a variety of cis or trans hydrindanes, decalins, and bicyclo[4.3.0]undecanes.
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Affiliation(s)
- Fraser F. Fleming
- Department of Chemistry and Biochemistry, Mellon Hall, Duquesne University, Pittsburgh PA 15282-1530, USA
| | - Subramanyham Gudipati
- Schering-Plough Research Institute, 2015 Galloping Hill Road, Kenilworth, N.J. 07033-0530, USA Fax: +1-908-740-7441
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Fleming FF, Wei Y, Liu W, Zhang Z. Metalated Nitriles: Stereodivergent Cation-Controlled Cyclizations1. Tetrahedron 2008; 64:7477-7488. [PMID: 19657380 PMCID: PMC2597827 DOI: 10.1016/j.tet.2008.05.110] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
Stereodivergent cyclizations of gamma-hydroxy cyclohexanecarbonitriles are controlled simply through judicious choice of cation in the alkylmetal base. Deprotonating a series of cyclic gamma-hydroxy nitriles with i-PrMgBr generates C-magnesiated nitriles that cyclize under stereoelectronic control to cis-fused hydrindanes, decalins, and bicyclo [5.4.0] undecanes. An analogous deprotonation with BuLi triggers cyclization to trans-fused hydrindanes, decalins, and bicyclo [5.4.0] undecanes consistent with a sterically controlled electrophilic attack on an equatorial nitrile anion. Using cations to control the geometry of metalated nitriles provides a versatile, stereodivergent cyclization to cis- and trans-hydrindanes, decalins, and [5. 4. 0] undecanes, and reveals the key geometric requirements for intramolecular S(N)2 and S(N)2' displacements.
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Affiliation(s)
- Fraser F. Fleming
- Department of Chemistry and Biochemistry, Duquesne University, Pittsburgh, Pennsylvania 15282-1530,
| | - Yunjing Wei
- Department of Chemistry and Biochemistry, Duquesne University, Pittsburgh, Pennsylvania 15282-1530,
| | - Wang Liu
- Department of Chemistry and Biochemistry, Duquesne University, Pittsburgh, Pennsylvania 15282-1530,
| | - Zhiyu Zhang
- Department of Chemistry and Biochemistry, Duquesne University, Pittsburgh, Pennsylvania 15282-1530,
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Sasaki M, Kawanishi E, Shirakawa Y, Kawahata M, Masu H, Yamaguchi K, Takeda K. Chirality Transfer from Epoxide to Carbanion: Base-Induced Alkylation ofO-Carbamoyl Cyanohydrins of β-Silyl-α,β-epoxy Aldehyde. European J Org Chem 2008. [DOI: 10.1002/ejoc.200800300] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
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Fleming FF, Wei G, Steward OW. Cyclic nitriles: stereodivergent addition-alkylation-cyclization to cis- and trans-abietanes. J Org Chem 2008; 73:3674-9. [PMID: 18416532 DOI: 10.1021/jo8001062] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Diverse cyclic hydroxy nitriles are readily synthesized through sequential 1,2-1,4-Grignard addition-methylations to 3-oxo-1-cyclohexene-1-carbonitrile. Acid-catalyzed intramolecular cyclizations of the cyclic hydroxy nitriles reveal fundamental stereoselectivity trends in Friedel-Crafts cyclizations to cis- and trans-abietanes. In contrast to previous assumptions, comparative cationic cyclizations with electron-rich and electron-poor aromatic nucleophiles exhibit similar preferences for cyclization to cis-abietanes. Optimizing the cyclizations for trans-abietanes has identified ZrCl 4 as an exceptional Lewis acid which, for cyclizations of iminolactones, favors trans-abietanes as the only observable diastereomer. The sequential oxonitrile addition-Friedel-Crafts cyclization strategy provides a rapid, stereodivergent synthesis of cis- or trans-abietanes, demonstrates the dramatic influence of ZrCl 4 in promoting cationic cyclizations, and in contrast to previous assumptions suggests that the cyclization stereoselectivity is not correlated with the electronic nature of the aromatic nucleus.
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Affiliation(s)
- Fraser F Fleming
- Department of Chemistry and Biochemistry, Duquesne University, Pittsburgh, PA 15282-1530, USA.
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Fleming FF, Liu W, Ghosh S, Steward OW. Metalated Nitriles: Internal 1,2-Asymmetric Induction. J Org Chem 2008; 73:2803-10. [DOI: 10.1021/jo702681e] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Fraser F. Fleming
- Department of Chemistry and Biochemistry, Duquesne University, Pittsburgh, Pennsylvania 15282-1530
| | - Wang Liu
- Department of Chemistry and Biochemistry, Duquesne University, Pittsburgh, Pennsylvania 15282-1530
| | - Somraj Ghosh
- Department of Chemistry and Biochemistry, Duquesne University, Pittsburgh, Pennsylvania 15282-1530
| | - Omar W. Steward
- Department of Chemistry and Biochemistry, Duquesne University, Pittsburgh, Pennsylvania 15282-1530
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Gibson HW, Berg MAG, Dickson JC, Lecavalier PR, Wang H, Merola JS. Diastereomeric Reissert Compounds of Isoquinoline and 6,7-Dimethoxy-3,4-dihydroisoquinoline in Stereoselective Synthesis. J Org Chem 2007; 72:5759-70. [PMID: 17592876 DOI: 10.1021/jo070786k] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Chiral acid chlorides were reacted with isoquinoline and 6,7-dimethoxy-3,4-dihydroisoquinoline to form diastereomeric Reissert compounds 8-11 and 18-21, respectively. The best diastereoselectivity (80:20) was achieved in formation of the 9-phenylmenthyl derivative 20. The diastereomers of 2-l-menthoxycarbonyl-1,2-dihydroisoquinaldonitriles (S)-8/(R)-8), formed in equal amounts, were inseparable. However, the individual diastereomers of 2-cholesteryloxycarbonyl-1,2-dihydroisoquinaldonitriles ((R)-11 and (S)-11) and the 2-l-menthoxycarbonyl-6,7-dimethoxy-1,2,3,4-tetrahydroisoquinaldonitriles ((S)-19/(R)-19)) were each readily purified. (S)-8/(R)-8 (1:1) via the corresponding anions (NaH, -40 degrees C, DMF) with pivaldehyde yielded in 82:18 predominance the S-diastereomer of 1-isoquinolyl tert-butyl carbinyl l-menthyl carbonate ((S)-12), which was obtained in pure form by a single recrystallization; hydrolysis produced 99% pure S-(-)-1-isoquinolyl tert-butyl carbinol [(S)-16]. Reactions of the anions of diastereomeric Reissert compounds, either as mixtures or pure single species, with aromatic aldehydes and alkyl halides proceeded with at best modest selectivity (diastereomeric ratios up to 66:34 and 72:28, respectively). Therefore, it is concluded that the Reissert anions are either planar or rapidly inverting tetrahedral structures.
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Affiliation(s)
- Harry W Gibson
- Department of Chemistry, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061, USA.
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Fleming FF, Vu VA, Shook BC, Rahman M, Steward OW. Metalated Nitriles: Chelation-Controlled Cyclizations to cis and trans Hydrindanes and Decalins. J Org Chem 2007; 72:1431-6. [PMID: 17249734 DOI: 10.1021/jo062270r] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Chelation provides a powerful means of stereocontrol in alkylations of metalated nitriles. Doubly deprotonating a series of cyclic beta-hydroxynitriles triggers cyclizations that implicate metalated nitrile intermediates having configurations imposed by chelation with an adjacent, chiral lithium alkoxide. Identifying chelation as a general stereocontrol element explains several previously anomalous alkylations of metalated nitriles and provides a potential solution to the long-standing difficulty of synthesizing trans-hydrindanes. Employing chelation to control the metalated nitrile geometry permits selective cyclizations to cis and trans hydrindanes and decalins and provides key insight into the geometrical requirements of these demanding cyclizations.
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Affiliation(s)
- Fraser F Fleming
- Department of Chemistry and Biochemistry, Duquesne University, Pittsburgh, PA 15282-1530, USA.
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Fleming FF, Gudipati S, Zhang Z, Liu W, Steward OW. Cyclic Nitriles: Diastereoselective Alkylations. J Org Chem 2005; 70:3845-9. [PMID: 15876069 DOI: 10.1021/jo0501184] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
[reaction: see text] Diastereoselective alkylations of metalated conformationally locked 4-tert-butylcyclohexanecarbonitrile are highly diastereoselective with magnesium and copper counterions but only modestly diastereoselective with lithium as the counterion. Selective generation of diverse metalated nitriles is readily achieved through bromine-magnesium, -copper, and -lithium exchange reactions of the corresponding bromonitrile or, for lithium, by deprotonating the parent nitrile with lithium diethylamide. Collectively, high alkylation stereoselectivities correlate with the retentive alkylations of C-metalated nitriles, whereas N-lithiated nitriles alkylate with modest selectivity, reflecting minimal steric differences in the corresponding axial and equatorial electrophile trajectories.
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Affiliation(s)
- Fraser F Fleming
- Department of Chemistry and Biochemistry, Duquesne University, Pittsburgh, Pennsylvania 15282-1530, USA.
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Fleming FF, Zhang Z, Liu W, Knochel P. Metalated Nitriles: Organolithium, -magnesium, and -copper Exchange of α-Halonitriles. J Org Chem 2005; 70:2200-5. [PMID: 15760206 DOI: 10.1021/jo047877r] [Citation(s) in RCA: 52] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
[reaction: see text] alpha-Halonitriles react with alkyllithium, organomagnesium, and lithium dimethylcuprate reagents generating reactive, metalated nitriles. The rapid halogen-metal exchange with alkyllithium and Grignard reagents allows selective exchange in the presence of reactive carbonyl electrophiles, including aldehydes, providing a high-yielding alkylation protocol. Lithiated and magnesiated nitriles react with propargyl bromide by S(N)2 displacement whereas organocopper nitriles react by S(N)2' displacement, correlating with the formation of a C-metalated nitrile.
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Affiliation(s)
- Fraser F Fleming
- Department of Chemistry and Biochemistry, Duquesne University, Pittsburgh, Pennsylvania 15282-1530, USA.
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Fleming FF, Zhang Z, Knochel P. Metalated Nitriles: Halogen−Metal Exchange with α-Halonitriles. Org Lett 2004; 6:501-3. [PMID: 14961608 DOI: 10.1021/ol036202s] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
[reaction: see text] Alpha-halonitriles react with organometallic reagents in a facile halogen-metal exchange. The halogen-metal exchange is extremely fast with Grignard and alkyllithium reagents, generating metalated nitriles in situ with aldehyde, ketone, acid chloride, and acyl cyanide electrophiles. Sequential halogen-metal exchange and methylation of conformationally constrained nitriles is highly stereoselective and consistent with a retentive alkylation of a C-magnesiated nitrile.
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Affiliation(s)
- Fraser F Fleming
- Department of Chemistry and Biochemistry, Duquesne University, Pittsburgh, Pennsylvania 15282-1530, USA.
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