DOCSLIB.ORG

Asymmetric Ylide Reactions: Epoxidation, Cyclopropanation, Aziridination, Olefination, and Rearrangement†

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Asymmetric Ylide Reactions: Epoxidation, Cyclopropanation, Aziridination, Olefination, and Rearrangement† Chem. Rev. 1997, 97, 2341−2372 2341 Asymmetric Ylide Reactions: Epoxidation, Cyclopropanation, Aziridination, Olefination, and Rearrangement† An-Hu Li and Li-Xin Dai* Laboratory of Organometallic Chemistry, Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences, 354 Fenglin Lu, Shanghai 200032, China Varinder K. Aggarwal Department of Chemistry, Dainton Building, The University of Sheffield, Sheffield S3 7HF, The United Kingdom Received March 10, 1997 (Revised Manuscript Received May 28, 1997) Contents Scheme 1 I. Introduction 2341 II. Asymmetric Epoxidations 2342 A. Reagent-Controlled Asymmetric Epoxidations 2342 1. Chiral Aminosulfoxonium Ylides 2343 2. Chiral Sulfonium Ylides 2343 3. Chiral Arsonium Ylides 2346 4. Other Related Reagents 2347 B. Substrate-Controlled Asymmetric Epoxidations 2347 C. Related Reactions 2349 III. Asymmetric Cyclopropanations 2350 A. Reagent-Controlled Asymmetric 2351 Cyclopropanations 1. Chiral Aminosulfoxonium Ylides 2351 2. Other Ylides and Related Reagents 2351 B. Substrate-Controlled Asymmetric 2352 Cyclopropanations 1. Chiral R,â-Unsaturated Bicyclic 2352 γ-Lactams 2. L-Tartaric Acid- and 2354 D-Glyceraldehyde-Derived R,â-Unsaturated Esters 3. Other Chiral R,â-Unsaturated Compounds 2355 IV. Asymmetric Aziridinations 2356 A. Reagent-Controlled Asymmetric Aziridinations 2356 only realized after the birth of Wittig reaction in B. Substrate-Controlled Asymmetric 2357 1953.1 Since then, the chemistry of ylides grew Aziridinations rapidly and they have now become powerful and V. Asymmetric Rearrangements 2358 versatile synthetic tools in the arsenal of organic A. [2,3]-σ-Rearrangements 2358 chemists. In addition to the synthetically important 1. Allylic and Propargylic Sulfonium and 2358 phosphonium2 and sulfonium3 ylides, ylides of Oxonium Ylides other heteroatoms,4 namely ammonium,5 azo- 2. Allylic Ammonium Ylides 2362 methine,6 pyridinium,7 nitrile,8 aminosulfoxonium,9 B. Other Rearrangements 2363 thiophenium,10 thiocarbonyl,6c,6f carbonyl,8,11 As,12 VI. Asymmetric Olefinations 2367 Sb,12a,b,13 Bi,12a,b Se,14 Te,14a,15 Ge,16 Sn,16 and I17 have A. Desymmetrization 2367 been developed and reviewed in recent years. B. Kinetic and Dynamic Kinetic Resolutions of 2368 An ylide can be viewed as a special carbanion, Racemic Carbonyl Compounds which bears a neighboring positively charged het- C. Preparation of Chiral Allenes 2369 eroatom. Ylides undergo three types of reactions: VII. Concluding Remarks 2369 olefination, cyclization to a three-membered ring VIII. Acknowledgments 2369 (epoxidation, cyclopropanation or aziridination), and IX. References 2370 rearrangement reactions ([2,3]-σ-rearrangement or Stevens rearrangement) as shown in Scheme 1. The reaction of an ylide with an electrophilic carbon atom I. Introduction of a CdX(X)O, C, N) bond (carbonyl compounds, Although the first ylide appeared as early as the † Dedicated to Professor Yao-Zeng Huang on the occasion of his 1900s, the recognition of these structurally interest- 85th birthday and for his significant contributions to the ylide ing compounds as synthetically useful reagents was chemistry. S0009-2665(96)00411-6 CCC: $28.00 © 1997 American Chemical Society 2342 Chemical Reviews, 1997, Vol. 97, No. 6 Li et al. An-Hu Li was born in Sichuan Province, China, in 1968. He received his Varinder Kumar Aggarwal was born in Kalianpur (a small village in the B.A. (1990) from Sichuan Normal University, M.S. (1993) from Lanzhou state of Punjab) in North India in 1961 and emigrated to the United Institute of Chemical Physics, Chinese Academy of Sciences, and Ph.D. Kingdom in 1963. He received his B.A. (1983) and Ph.D. (1986) from (1996) from SIOC, the last under the guidance of Professor Li-Xin Dai. Cambridge University, the latter under the guidance of Dr. Stuart Warren. He has been a research assistant in Professor Dai’s group at SIOC for He was subsequently awarded a Harkness Fellowship and carried out one year since receiving his Ph.D. degree and is now in Dr. Kenneth A. postdoctoral work with Professor Gilbert Stork at Columbia University, Jacobson’s group at NIDDK/NIH, Bethesda, MD, for his postdoctoral NY (1986−1988). He returned to a lectureship at Bath University and in research. His research interests are in synthetic methodology, asymmetric 1991 moved to Sheffield University where he is currently Reader in synthesis, and ylide chemistry. Chemistry. His research interests are in synthetic organic chemistry and asymmetric synthesis. II. Asymmetric Epoxidations The notable biological significance20 and various chemical transformations21 of nonracemic epoxides make them one of the most useful synthetic inter- mediates.22 They can be prepared by either enanti- oselective oxidation of a prochiral CdC bond (route a) or by enantioselective alkylidenation of a prochiral CdO bond, such as via an ylide, carbene, or a Darzens reaction (route b) (Scheme 2). Although the Scheme 2 Li-Xin Dai was born in Beijing, China, in 1924. He received his B.A. from Zhejiang University in 1947. He has been assistant professor, associate professor, and full professor of Shanghai Institute of Organic Chemistry (SIOC) since 1953 and was elected as a Member of Chinese Academy of Sciences in 1993. He is now the Vice President of the Academic Committee of SIOC and the President of the Academic Committee of Laboratory of Organometallic Chemistry, Chinese Academy of Sciences. His research interests are focusing on synthetic methodology and asymmetric synthesis. Michael acceptors or imines) gives a betaine or oxidation method has proved overwhelmingly suc- oxetane intermediate. From this intermediate, elimi- cessful,23 the structural requirements of the sub- nation of the heteroatom-containing group can occur strates are a limiting prerequisite: the Sharpless in either one of two different modes resulting in asymmetric epoxidation23a requires allylic alcohols; cyclization or olefination. the Jacobsen method23b only works well with cis The exploration of asymmetric ylide reactions using double bonds; and the dioxirane method good for 23c-e a chiral ylide or a chiral CdX compound began in some trans olefins. The ylide route provides an the early 1960s, and many results have been reported alternative nonoxidative approach to prepare opti- in the field of asymmetric reactions via an ylide route cally active epoxides and many results have appeared over the last 30 years. Although several related in recent years. These will be discussed in two summaries were documented in specialized areas, parts: reagent-controlled and substrate-controlled like cyclopropanation,9,18 epoxidation,9 and [2,3]-σ- ylide asymmetric epoxidations. rearrangement,19 a comprehensive review on asym- metric ylide reaction has not appeared yet. The A. Reagent-Controlled Asymmetric Epoxidations present review aims to summarize the recent work The reaction of a chiral ylide reagent with an in the field of asymmetric ylide reactions, with achiral aldehyde or ketone will give a chiral epoxide respect to epoxidations, cyclopropanations, aziridi- with the recovery of chiral ylide precursor, which can nations, [2,3]-σ-rearrangements, and olefinations. usually be reconverted into the ylide reagent (Scheme Asymmetric Ylide Reactions Chemical Reviews, 1997, Vol. 97, No. 6 2343 Scheme 3 Scheme 6 3). The intermediates used in asymmetric epoxida- tion include sulfonium, aminosulfoxonium, and ar- sonium ylides. Most work has centered around the use of sulfonium ylides and excellent results have been obtained when these intermediates were used. 1. Chiral Aminosulfoxonium Ylides A. W. Johnson24 first showed that the sulfonium Scheme 7 ylides could be used to prepare oxiranes. While it is questionable whether tetrahedral sulfonium ylides can racemize,25,26 there is no dispute about the configurational stability of aminosulfoxonium ylides. Carl Johnson first prepared enantiomerically pure ylide (R)-(-)-3 starting from sulfoxide (R)-(+)-1 and when reacted with benzaldehyde gave (R)-styrene oxide in 20% ee (Scheme 4).9,27-30 Reaction of ylide Scheme 4 cyclopropane was formed. In contrast, treatment of sulfide 11 with MeI followed by base gave styrene oxide in 90% ee. As alkylation of sulfide 11 gave a mixture of diastereomers; reverse betaine formation would have produced a mixture of enantiomeric ylides which could not have produced such high levels of enantiomeric excess. It was therefore concluded that the intermediate betaine from sulfonium ylides was formed irreversibly. Although asymmetric epoxidations using amino- sulfoxonium ylides have not been extensively ex- plored, the work shown above demonstrated for the 4 with heptaldehyde gave the corresponding epoxide first time that nonracemic epoxides could be obtained with opposite enantioselectivity as expected.27,28 The via chiral ylides. mechanism of epoxidation was investigated. Assum- ing a two-step mechanism for epoxidation, ylides can 2. Chiral Sulfonium Ylides react reversibly or irreversibly with carbonyl com- pounds (step 1) prior to irreversible ring closure (step The relative ease of preparation and versatility in 2) (Scheme 5). To probe whether ylide additions to epoxidation reactions of chiral sulfonium ylides make them the more useful ones than aminosulfoxonium Scheme 5 ylides in the preparation of nonracemic epoxides. Sulfonium salts and their corresponding ylides are tetrahedral and are thus capable of exhibiting optical activity.25,26 Sulfonium salts can racemize by inver- sion (and other mechanisms), but the barrier is relatively high and
Load more

Recommended publications
  • Supporting Information a Convenient Chromatography-Free Method For
    Electronic Supplementary Material (ESI) for Organic & Biomolecular Chemistry This journal is © The Royal Society of Chemistry 2012 Supporting Information A Convenient Chromatography-Free Method for the Purification of Alkenes Produced in the Wittig Reaction Peter A. Byrne, Kamalraj V. Rajendran, Jimmy Muldoon and Declan G. Gilheany Centre for Synthesis and Chemical Biology, School of Chemistry and Chemical Biology, University College Dublin, Belfield, Dublin 4, Ireland 1. General Experimental 2 2. Synthesis of phosphonium salts 4 3. Procedures for Wittig reactions & phosphine oxide removal 11 4. Characterisation of purified alkenes 15 5. Reduction of phosphine chalcogenides 34 6. Synthesis & isolation of neomenthyl chloride and reduction of phosphine oxide-by-product 37 7. NMR spectra of phosphonium salts 42 8. NMR spectra of purified alkenes and regenerated phosphines from Wittig reactions 56 9. NMR spectra of phosphines produced by reduction of phosphine chalcogenides 85 10. NMR spectra of purified products from Appel-type reactions 90 11. References 91 1 Electronic Supplementary Material (ESI) for Organic & Biomolecular Chemistry This journal is © The Royal Society of Chemistry 2012 1. General Experimental All chemicals were supplied by Aldrich, with the exception of Zeoprep silica, 2- methylbenzaldehyde ( o-tolualdehyde, Fluka), ( tert -butoxycarbonylmethyl)- -1 triphenylphosphonium bromide (Fluka), 1 mol L LiAlH 4 in THF (Acros Organics) and Merck standardised alumina 90. All chemicals were used without further purification except diethyl ether, toluene, and THF, which were processed through an Innovative Technology Inc. Pure Solv-400-3-MD solvent purification (Grubbs still) system and stored in Strauss flasks under a nitrogen atmosphere, and ethyl acetate and dichloromethane, which were degassed by passing a stream of dry nitrogen gas (oxygen- free) through the solvent for one hour for the purposes of work-ups in phosphine syntheses.
    [Show full text]
  • Synthesis of Indole and Oxindole Derivatives Incorporating Pyrrolidino, Pyrrolo Or Imidazolo Moieties
    From DEPARTMENT OF BIOSCIENCES AT NOVUM Karolinska Institutet, Stockholm, Sweden SYNTHESIS OF INDOLE AND OXINDOLE DERIVATIVES INCORPORATING PYRROLIDINO, PYRROLO OR IMIDAZOLO MOIETIES Stanley Rehn Stockholm 2004 All previously published papers have been reproduced with permission from the publishers. Published and printed by Karolinska University Press Box 200, SE-171 77 Stockholm, Sweden © Stanley Rehn, 2004 ISBN 91-7140-169-5 Till Amanda Abstract The focus of this thesis is on the synthesis of oxindole- and indole-derivatives incorporating pyrrolidins, pyrroles or imidazoles moieties. Pyrrolidino-2-spiro-3’-oxindole derivatives have been prepared in high yielding three-component reactions between isatin, α-amino acid derivatives, and suitable dipolarophiles. Condensation between isatin and an α-amino acid yielded a cyclic intermediate, an oxazolidinone, which decarboxylate to give a 1,3-dipolar species, an azomethine ylide, which have been reacted with several dipolarophiles such as N- benzylmaleimide and methyl acrylate. Both N-substituted and N-unsubstituted α- amino acids have been used as the amine component. 3-Methyleneoxindole acetic acid ethyl ester was reacted with p- toluenesulfonylmethyl isocyanide (TosMIC) under basic conditions which gave (in a high yield) a colourless product. Two possible structures could be deduced from the analytical data, a pyrroloquinolone and an isomeric ß-carboline. To clarify which one of the alternatives that was actually formed from the TosMIC reaction both the ß- carboline and the pyrroloquinolone were synthesised. The ß-carboline was obtained when 3-ethoxycarbonylmethyl-1H-indole-2-carboxylic acid ethyl ester was treated with a tosylimine. An alternative synthesis of the pyrroloquinolone was performed via a reduction of a 2,3,4-trisubstituted pyrrole obtained in turn by treatment of a vinyl sulfone with ethyl isocyanoacetate under basic conditions.
    [Show full text]
  • Visible Light Photoredox Catalysis with Transition Metal Complexes: Application in Organic Synthesis
    Visible Light Photoredox Catalysis with Transition Metal Complexes: Application in Organic Synthesis Penghao Chen Dong Group Seminar April, 10th, 2013 Introduction Kalyanasundaram, K. Coord. Chem. Rev. 1982, 46, 159 Introduction Stern‐Volmer Relationship Turro, N. J. Modern Molecular Photochemistry; Benjamin/Cummings: Menlo Park, CA, 1978. Stoichiometric Net Reductive Reactionreductant1. Reduction is required of Electron Poor Olefin O Bn NH2 2 Pac, C. et. al., J. Am. Chem. Soc. 1981, 103, 6495 Net Reductive Reaction 2. Reductive Dehalogenation Fukuzumi, S. et. al., J. Phys. Chem. 1990, 94, 722. Net Reductive Reaction 2. Reductive Dehalogenation Stephenson, C. R. J. et. al., J. Am. Chem. Soc. 2009, 131, 8756. Stephenson, C. R. J. et. al., Nature Chem. 2012, 4, 854 Net Reductive Reaction 3. Radical Cyclization Stephenson, C. R. J. et. al., Chem. Commun. 2010, 46, 4985 Stephenson, C. R. J. et. al., Nature Chem. 2012, 4, 854 Net Reductive Reaction 4. Epoxide and Aziridine Opening Fensterbank, L. et. al., Angew. Chem., Int. Ed. 2011, 50, 4463 Hasegawa, E. et. al., Tetrahedron 2006, 62, 6581 Guindon, Y. et. al., Synlett 1998, 213 Guindon, Y. et. al., Synlett 1995, 449 Net Oxidative Reaction 1. Functional Group Reactions Cano‐Yelo, H.; Deronzier, A. Tetrahedron Lett. 1984, 25, 5517 Net Oxidative Reaction 1. Functional Group Reactions Jiao, N. et. al., Org. Lett. 2011, 13, 2168 Net Oxidative Reaction 1. Functional Group Reactions Jørgensen, K. A.; Xiao, W.‐J. Angew. Chem., Int. Ed. 2012, 51, 784 Net Oxidative Reaction 2. Oxid. Generation of Iminium Ions Stephenson, C. R. J. et. al., J. Am. Chem. Soc. 2010, 132, 1464 Net Oxidative Reaction 2.
    [Show full text]
  • Priya Mathew
    PROGRESS TOWARDS THE TOTAL SYNTHESIS OF MITOMYCIN C By Priya Ann Mathew Dissertation Submitted to the Faculty of the Graduate School of Vanderbilt University in partial fulfillment of the requirements for the degree of DOCTOR OF PHILOSOPHY in Chemistry August, 2012 Nashville, Tennessee Approved: Professor Jeffrey N. Johnston Professor Brian O. Bachmann Professor Ned A. Porter Professor Carmelo J. Rizzo ACKNOWLEDGMENTS I would like to express my gratitude to everyone who made my graduate career a success. Firstly, I would like to thank my advisor, Professor Jeffrey Johnston, for his dedication to his students. He has always held us to the highest standards and he does everything he can to ensure our success. During the challenges we faced in this project, he has exemplified the true spirit of research, and I am especially grateful to him for having faith in my abilities even when I did not. I would like to acknowledge all the past and present members of the Johnston group for their intellectual discussion and their companionship. In particular, I would like to thank Aroop Chandra and Julie Pigza for their incredible support and guidance during my first few months in graduate school, Jayasree Srinivasan who worked on mitomycin C before me, and Anand Singh whose single comment “A bromine is as good as a carbon!” triggered the investigations detailed in section 2.6. I would also like to thank the other members of the group for their camaraderie, including Jessica Shackleford and Amanda Doody for their friendship, Hubert Muchalski for everything related to vacuum pumps and computers, Michael Danneman and Ken Schwieter for always making me laugh, and Matt Leighty and Ki Bum Hong for their useful feedback.
    [Show full text]
  • Supporting Information
    Electronic Supplementary Material (ESI) for RSC Advances. This journal is © The Royal Society of Chemistry 2021 Supporting Information Synthesis, Oligomerization and Catalytic Studies of a Redox- Active Ni4-Cubane: A detailed Mechanistic Investigation Saroj Kumar Kushvaha, a† Maria Francis, b† Jayasree Kumar, a Ekta Nag, b Prathap Ravichandran, a b a Sudipta Roy* and Kartik Chandra Mondal* aDepartment of Chemistry, Indian Institute of Technology Madras, Chennai 600036, India. bDepartment of Chemistry, Indian Institute of Science Education and Research (IISER) Tirupati 517507, India. † Both authors contributed equally. Table of Contents 1. General remarks 2. Syntheses of complexes 1-3 3. Detail characterization of complexes 1-3 4. Computational details 5. X-ray single crystal diffraction of complexes 1-3. 6. Details of catalytic activities of complex 3 6.1. General procedures for the syntheses of aromatic heterocycles (6) and various diazoesters (7) 6.2. Optimization of reaction condition for cyclopropanation of aromatic heterocycles (6) 6.3. General synthetic procedure and characterization data for cyclopropanated aromatic heterocycles (8) 6.4. Determination of relative stereochemistry of 8 7. 1H and 13C NMR spectra of compounds 8a-j 8. Mechanistic investigations and mass spectrometric analysis 9. References S1 1. General remarks All catalytic reactions were performed under Argon atmosphere. The progress of all the catalytic reactions were monitored by thin layer chromatography (TLC, Merck silica gel 60 F 254) upon visualization of the TLC plate under UV light (250 nm). Different charring reagents, such as phosphomolybdic acid/ethanol, ninhydrin/acetic acid solution and iodine were used to visualize various starting materials and products spots on TLC plates.
    [Show full text]
  • Gold-Catalyzed Ethylene Cyclopropanation
    Gold-catalyzed ethylene cyclopropanation Silvia G. Rull, Andrea Olmos* and Pedro J. Pérez* Full Research Paper Open Access Address: Beilstein J. Org. Chem. 2019, 15, 67–71. Laboratorio de Catálisis Homogénea, Unidad Asociada al CSIC, doi:10.3762/bjoc.15.7 CIQSO-Centro de Investigación en Química Sostenible and Departamento de Química, Universidad de Huelva, Campus de El Received: 17 October 2018 Carmen 21007 Huelva, Spain Accepted: 11 December 2018 Published: 07 January 2019 Email: Andrea Olmos* - [email protected]; Pedro J. Pérez* - This article is part of the thematic issue "Cyclopropanes and [email protected] cyclopropenes: synthesis and applications". * Corresponding author Guest Editor: M. Tortosa Keywords: © 2019 Rull et al.; licensee Beilstein-Institut. carbene transfer; cyclopropane; cyclopropylcarboxylate; ethylene License and terms: see end of document. cyclopropanation; ethyl diazoacetate; gold catalysis Abstract Ethylene can be directly converted into ethyl 1-cyclopropylcarboxylate upon reaction with ethyl diazoacetate (N2CHCO2Et, EDA) F F in the presence of catalytic amounts of IPrAuCl/NaBAr 4 (IPr = 1,3-bis(2,6-diisopropylphenyl)imidazole-2-ylidene; BAr 4 = tetrakis(3,5-bis(trifluoromethyl)phenyl)borate). Introduction Nowadays the olefin cyclopropanation through metal-catalyzed carbene transfer starting from diazo compounds to give olefins constitutes a well-developed tool (Scheme 1a), with an exquisite control of chemo-, enantio- and/or diastereoselectiv- ity being achieved [1,2]. Previous developments have involved a large number of C=C-containing substrates but, to date, the methodology has not been yet employed with the simplest olefin, ethylene, for synthetic purposes [3]. Since diazo compounds bearing a carboxylate substituent are the most Scheme 1: (a) General metal-catalyzed olefin cyclopropanation reac- commonly employed carbene precursors toward olefin cyclo- tion with diazo compounds.
    [Show full text]
  • Bond Distances and Bond Orders in Binuclear Metal Complexes of the First Row Transition Metals Titanium Through Zinc
    Metal-Metal (MM) Bond Distances and Bond Orders in Binuclear Metal Complexes of the First Row Transition Metals Titanium Through Zinc Richard H. Duncan Lyngdoh*,a, Henry F. Schaefer III*,b and R. Bruce King*,b a Department of Chemistry, North-Eastern Hill University, Shillong 793022, India B Centre for Computational Quantum Chemistry, University of Georgia, Athens GA 30602 ABSTRACT: This survey of metal-metal (MM) bond distances in binuclear complexes of the first row 3d-block elements reviews experimental and computational research on a wide range of such systems. The metals surveyed are titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, and zinc, representing the only comprehensive presentation of such results to date. Factors impacting MM bond lengths that are discussed here include (a) n+ the formal MM bond order, (b) size of the metal ion present in the bimetallic core (M2) , (c) the metal oxidation state, (d) effects of ligand basicity, coordination mode and number, and (e) steric effects of bulky ligands. Correlations between experimental and computational findings are examined wherever possible, often yielding good agreement for MM bond lengths. The formal bond order provides a key basis for assessing experimental and computationally derived MM bond lengths. The effects of change in the metal upon MM bond length ranges in binuclear complexes suggest trends for single, double, triple, and quadruple MM bonds which are related to the available information on metal atomic radii. It emerges that while specific factors for a limited range of complexes are found to have their expected impact in many cases, the assessment of the net effect of these factors is challenging.
    [Show full text]
  • Catalytic Cyclopropanation of Polybutadienes
    Erschienen in: Journal of Polymer Science, Part A: Polymer Chemistry ; 48 (2010), 20. - S. 4439-4444 https://dx.doi.org/10.1002/pola.24231 Catalytic Cyclopropanation of Polybutadienes JUAN URBANO,1 BRIGITTE KORTHALS,2 M. MAR DI´AZ-REQUEJO,1 PEDRO J. PE´ REZ,1 STEFAN MECKING2 1Laboratorio de Cata´ lisis Homoge´ nea, Departamento de Quı´mica y Ciencia de los Materiales, Unidad Asociada al CSIC, Centro de Investigacio´ n en Quı´mica Sostenible, Campus de El Carmen s/n, Universidad de Huelva, 21007 Huelva, Spain 2Department of Chemistry, University of Konstanz, 78464 Konstanz, Germany ABSTRACT: Catalytic cyclopropanation of commercial 1,2- or 1,4- bonyl-cyclopropene)]. Catalytic hydrogenation of residual dou- cis-polybutadiene, respectively, with ethyl diazoacetate catalyzed ble bonds of partially cyclopropanated polybutadienes provided by [TpBr3Cu(NCMe)] (TpBr3 ¼ hydrotris(3,4,5-tribromo-1-pyrazo- access to the corresponding saturated polyolefins. Thermal lyl)borate) at room temperature afforded high molecular weight properties are reported. 5 À1 (Mn > 10 mol ) side-chain or main-chain, respectively, carbox- yethyl cyclopropyl-substituted polymers with variable and con- trolled degrees of functionalization. Complete functionalization KEYWORDS: carbene addition; catalysis; functionalization of poly- of 1,4-cis-polybutadiene afforded poly[ethylene-alt-(3-ethoxycar- mers; organometallic catalysis; polar groups; polybutadienes INTRODUCTION Catalytic insertion polymerization of ethyl- polypropylene.6 Examples of catalytic post-polymerization ene and propylene is employed for the production of more reactions on saturated polyolefins are rare. The oxyfunction- than 60 million tons of polyolefins annually.1 These poly- alization of polyethylenes and polypropylenes by metal- mers are hydrocarbons, without any heteroatom-containing based catalysts can afford hydroxyl groups.7 We have functional groups, such as for example ester moieties.
    [Show full text]
  • 19.13 the Wittig Alkene Synthesis 933
    19_BRCLoudon_pgs5-0.qxd 12/9/08 11:41 AM Page 933 19.13 THE WITTIG ALKENE SYNTHESIS 933 PROBLEMS 19.32 Draw the structures of all aldehydes or ketones that could in principle give the following product after application of either the Wolff–Kishner or Clemmensen reduction. H3C CH2CH(CH3)2 L L 19.33 Outline a synthesis of 1,4-dimethoxy-2-propylbenzene from hydroquinone (p-hydroxyphenol) and any other reagents. 19.13 THE WITTIG ALKENE SYNTHESIS Our tour through aldehyde and ketone chemistry started with simple additions; then addition followed by substitution (acetal formation); then additions followed by elimination (imine and enamine formation). Another addition–elimination reaction, called the Wittig alkene synthe- sis, is an important method for preparing alkenes from aldehydes and ketones. An example of the Wittig alkene synthesis is the preparation of methylenecyclohexane from cyclohexanone. 1 1 A | A | O CH_ 2 PPh3 CH2 Ph3P O _ (19.70) 1 + 3 anL ylid + L 1 3 triphenylphosphine cyclohexanone methylenecyclohexane oxide The Wittig synthesis is especially important because it gives alkenes in which the position of the double bond is unambiguous; in other words, the Wittig synthesis is completely regios- elective.Itcanbeusedforthepreparationofalkenesthatwouldbedifficulttoprepareby other reactions. For example, methylenecyclohexane, which is readily prepared by the Wittig synthesis (Eq. 19.70), cannot be prepared by dehydration of 1-methylcyclohexanol; 1- methylcyclohexene is obtained instead, because alcohol dehydration gives the alkene iso- mer(s) in which the double bond has the greatest number of alkyl substituents (Sec. 10.1). OH " H2SO4 " CH3 H2O CH3 L + 1-methylcyclohexene H2SO4 (19.71) A CH2 (little or none formed) methylenecyclohexane The nucleophile in the Wittig alkene synthesis is a type of ylid.
    [Show full text]
  • Dppm-Derived Phosphonium Salts and Ylides As Ligand Precursors for S-Block Organometallics
    Issue in Honor of Prof. Rainer Beckert ARKIVOC 2012 (iii) 210-225 Dppm-derived phosphonium salts and ylides as ligand precursors for s-block organometallics Jens Langer,* Sascha Meyer, Feyza Dündar, Björn Schowtka, Helmar Görls, and Matthias Westerhausen Institute of Inorganic and Analytical Chemistry, Friedrich-Schiller-University Jena Humboldtstraße 8, D-07743 Jena, Germany E-mail: [email protected] Dedicated to Professor Rainer Beckert on the Occasion of his 60th Birthday DOI: http://dx.doi.org/10.3998/ark.5550190.0013.316 Abstract The addition reaction of 1,1-bis(diphenylphosphino)methane (dppm) and haloalkanes R-X yields the corresponding phosphonium salts [Ph2PCH2PPh2R]X (1a: R = Me, X = I; 1b: R = Et, X = Br; 1c: R = iPr, X = I; 1d: R = CH2Mes, X = Br; 1e: R = tBu, X = Br). In case of the synthesis of 1e, [Ph2MePH]Br (3) was identified as a by-product. Deprotonation of 1 by KOtBu offers access to the corresponding phosphonium ylides [Ph2PCHPPh2R] (2a: R = Me; 2b: R = Et; 2c: R = iPr; 2d: R = CH2Mes) in good yields. Further deprotonation of 2a using n-butyllithium allows the isolation of the lithium complex [Li(Ph2PCHPPh2CH2)]n (4) and its monomeric tmeda adduct [(tmeda)Li(Ph2PCHPPh2CH2)] (4a). All compounds were characterized by NMR measurements and, except of 4, by X-ray diffraction experiments. Keywords: Phosphonium salt, phosphonium ylide, lithium, lithium phosphorus coupling Introduction Phosphonium ylides gained tremendous importance in organic chemistry, since Wittig and co- workers developed their alkene synthesis in the
    [Show full text]
  • Appendix I: Named Reactions Single-Bond Forming Reactions Co
    Appendix I: Named Reactions 235 / 335 432 / 533 synthesis / / synthesis Covered in Covered Featured in problem set problem Single-bond forming reactions Grignard reaction various Radical couplings hirstutene Conjugate addition / Michael reaction strychnine Stork enamine additions Aldol-type reactions (incl. Mukaiyama aldol) various (aldol / Claisen / Knoevenagel / Mannich / Henry etc.) Asymmetric aldol reactions: Evans / Carreira etc. saframycin A Organocatalytic asymmetric aldol saframycin A Pseudoephedrine glycinamide alkylation saframycin A Prins reaction Prins-pinacol reaction problem set # 2 Morita-Baylis-Hillman reaction McMurry condensation Gabriel synthesis problem set #3 Double-bond forming reactions Wittig reaction prostaglandin Horner-Wadsworth-Emmons reaction prostaglandin Still-Gennari olefination general discussion Julia olefination and heteroaryl variants within the Corey-Winter olefination prostaglandin Peterson olefination synthesis Barton extrusion reaction Tebbe olefination / other methylene-forming reactions tetrodotoxin hirstutene / Selenoxide elimination tetrodotoxin Burgess dehydration problem set # 3 Electrocyclic reactions and related transformations Diels-Alder reaction problem set # 1 Asymmetric Diels-Alder reaction prostaglandin Ene reaction problem set # 3 1,3-dipolar cycloadditions various [2,3] sigmatropic rearrangement various Cope rearrangement periplanone Claisen rearrangement hirstutene Oxidations – Also See Handout # 1 Swern-type oxidations (Swern / Moffatt / Parikh-Doering etc. N1999A2 Jones oxidation
    [Show full text]
  • Studies in Directed Catalytic Asymmetric Hydroboration of 1,2-Disubstituted Unsaturated Amide
    University of Nebraska - Lincoln DigitalCommons@University of Nebraska - Lincoln Student Research Projects, Dissertations, and Chemistry, Department of Theses - Chemistry Department Summer 7-2017 STUDIES IN DIRECTED CATALYTIC ASYMMETRIC HYDROBORATION OF 1,2-DISUBSTITUTED UNSATURATED AMIDE Shuyang Zhang University of Nebraska - Lincoln, [email protected] Follow this and additional works at: http://digitalcommons.unl.edu/chemistrydiss Part of the Organic Chemistry Commons Zhang, Shuyang, "STUDIES IN DIRECTED CATALYTIC ASYMMETRIC HYDROBORATION OF 1,2-DISUBSTITUTED UNSATURATED AMIDE" (2017). Student Research Projects, Dissertations, and Theses - Chemistry Department. 85. http://digitalcommons.unl.edu/chemistrydiss/85 This Article is brought to you for free and open access by the Chemistry, Department of at DigitalCommons@University of Nebraska - Lincoln. It has been accepted for inclusion in Student Research Projects, Dissertations, and Theses - Chemistry Department by an authorized administrator of DigitalCommons@University of Nebraska - Lincoln. STUDIES IN DIRECTED CATALYTIC ASYMMETRIC HYDROBORATION OF 1,2- DISUBSTITUTED UNSATURATED AMIDE by Shuyang Zhang A THESIS Presented to the Faculty of The Graduate College at the University of Nebraska In Partial Fulfillment of Requirements For the Degree of Master of Science Major: Chemistry Under the Supervision of Professor James M. Takacs Lincoln, Nebraska July 2017 DIRECTED CATALYTIC ASYMMETRIC HYDROBORATION OF 1,2- DISUBSTITUTED ALKENES Shuyang Zhang, M.S. University of Nebraska 2017 Advisor: Professor James M. Takacs The Rh-catalyzed, substrate directed catalytic asymmetric hydroboration of γ,δ-unsaturated amides provides a direct route to enantioenriched acyclic secondary γ- borylated carbonyl derivatives with high regio- and enantioselectivity. The catalytic condition optimization and substrate scope study is discussed, including the effects in catalytical asymmetric hydroboration on pre-installed chiral γ,δ-unsaturated amides.
    [Show full text]