Reactions of Alkenes
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Organic Chemistry
Wisebridge Learning Systems Organic Chemistry Reaction Mechanisms Pocket-Book WLS www.wisebridgelearning.com © 2006 J S Wetzel LEARNING STRATEGIES CONTENTS ● The key to building intuition is to develop the habit ALKANES of asking how each particular mechanism reflects Thermal Cracking - Pyrolysis . 1 general principles. Look for the concepts behind Combustion . 1 the chemistry to make organic chemistry more co- Free Radical Halogenation. 2 herent and rewarding. ALKENES Electrophilic Addition of HX to Alkenes . 3 ● Acid Catalyzed Hydration of Alkenes . 4 Exothermic reactions tend to follow pathways Electrophilic Addition of Halogens to Alkenes . 5 where like charges can separate or where un- Halohydrin Formation . 6 like charges can come together. When reading Free Radical Addition of HX to Alkenes . 7 organic chemistry mechanisms, keep the elec- Catalytic Hydrogenation of Alkenes. 8 tronegativities of the elements and their valence Oxidation of Alkenes to Vicinal Diols. 9 electron configurations always in your mind. Try Oxidative Cleavage of Alkenes . 10 to nterpret electron movement in terms of energy Ozonolysis of Alkenes . 10 Allylic Halogenation . 11 to make the reactions easier to understand and Oxymercuration-Demercuration . 13 remember. Hydroboration of Alkenes . 14 ALKYNES ● For MCAT preparation, pay special attention to Electrophilic Addition of HX to Alkynes . 15 Hydration of Alkynes. 15 reactions where the product hinges on regio- Free Radical Addition of HX to Alkynes . 16 and stereo-selectivity and reactions involving Electrophilic Halogenation of Alkynes. 16 resonant intermediates, which are special favor- Hydroboration of Alkynes . 17 ites of the test-writers. Catalytic Hydrogenation of Alkynes. 17 Reduction of Alkynes with Alkali Metal/Ammonia . 18 Formation and Use of Acetylide Anion Nucleophiles . -
Recent Advances in Titanium Radical Redox Catalysis
JOCSynopsis Cite This: J. Org. Chem. 2019, 84, 14369−14380 pubs.acs.org/joc Recent Advances in Titanium Radical Redox Catalysis Terry McCallum, Xiangyu Wu, and Song Lin* Department of Chemistry and Chemical Biology, Cornell University, Ithaca, New York 14853, United States ABSTRACT: New catalytic strategies that leverage single-electron redox events have provided chemists with useful tools for solving synthetic problems. In this context, Ti offers opportunities that are complementary to late transition metals for reaction discovery. Following foundational work on epoxide reductive functionalization, recent methodological advances have significantly expanded the repertoire of Ti radical chemistry. This Synopsis summarizes recent developments in the burgeoning area of Ti radical catalysis with a focus on innovative catalytic strategies such as radical redox-relay and dual catalysis. 1. INTRODUCTION a green chemistry perspective, the abundance and low toxicity of Ti make its complexes highly attractive as reagents and Radical-based chemistry has long been a cornerstone of 5 1 catalysts in organic synthesis. synthetic organic chemistry. The high reactivity of organic IV/III radicals has made possible myriad new reactions that cannot be A classic example of Ti -mediated reactivity is the reductive ring opening of epoxides. This process preferentially readily achieved using two-electron chemistry. However, the − high reactivity of organic radicals is a double-edged sword, as cleaves and functionalizes the more substituted C O bond, the selectivity of these fleeting intermediates can be difficult to providing complementary regioselectivity to Lewis acid control in the presence of multiple chemotypes. In addition, promoted epoxide reactions. The synthetic value of Ti redox catalysis has been highlighted by their many uses in total catalyst-controlled regio- and stereoselective reactions involv- 6−10 ing free-radical intermediates remain limited,2 and the synthesis (Scheme 1). -
Unusual Regioselectivity in the Opening of Epoxides by Carboxylic Acid Enediolates
Molecules 2008, 13, 1303-1311 manuscripts; DOI: 10.3390/molecules13061303 OPEN ACCESS molecules ISSN 1420-3049 www.mdpi.org/molecules Communication Unusual Regioselectivity in the Opening of Epoxides by Carboxylic Acid Enediolates Luis R. Domingo, Salvador Gil, Margarita Parra* and José Segura Department of Organic Chemistry, Universitat de València, Dr. Moliner 50, 46100 Burjassot, Spain. Fax +34(9)63543831; E-mails: [email protected]; [email protected]; [email protected] * Author to whom correspondence should be addressed; E-mail: [email protected] Received: 29 May 2008; in revised form: 5 June 2008 / Accepted: 6 June 2008 / Published: 9 June 2008 Abstract: Addition of carboxylic acid dianions appears to be a potential alternative to the use of aluminium enolates for nucleophilic ring opening of epoxides. These conditions require the use of a sub-stoichiometric amount of amine (10% mol) for dianion generation and the previous activation of the epoxide with LiCl. Yields are good, with high regioselectivity, but the use of styrene oxide led, unexpectedly, to a mixture resulting from the attack on both the primary and secondary carbon atoms. Generally, a low diastereoselectivity is seen on attack at the primary center, however only one diastereoisomer was obtained from attack to the secondary carbon of the styrene oxide. Keywords: Lactones, lithium chloride, nucleophilic addition, regioselectivity, diastereoselectivity. Introduction Epoxides have been recognized among the most versatile compounds in organic synthesis, not only as final products [1] but as key intermediates for further manipulations. Accordingly, new synthetic developments are continuously being published [2]. Due to its high ring strain (around 27 Kcal/mol) its ring-opening, particularly with carbon-based nucleophiles, is a highly valuable synthetic strategy Molecules 2008, 13 1304 [3]. -
Highly Efficient Epoxidation of Olefins with Hydrogen Peroxide Oxidant Using Modified Silver Polyoxometalate Catalysts
African Journal of Pure and Applied Chemistry Vol. 7(2), pp. 50-55, February 2013 Available online at http://www.academicjournals.org/AJPAC DOI: 10.5897/AJPAC12.060 ISSN 1996 - 0840 ©2013 Academic Journals Full Length Research Paper Highly efficient epoxidation of olefins with hydrogen peroxide oxidant using modified silver polyoxometalate catalysts Emmanuel Tebandeke 1*, Henry Ssekaalo 1 and Ola F. Wendt 2 1Department of Chemistry, Makerere University, P. O. Box 7062 Kampala, Uganda. 2Organic Chemistry, Department of Chemistry, Lund University, P. O. Box 124, 221 00 Lund, Sweden. Accepted 31 January, 2013 The catalytic epoxidation of olefins is an important reaction in chemical industry since epoxides are versatile and important intermediates in the synthesis of fine chemicals and pharmaceuticals. The current epoxidation procedures often use stoichiometric organic and sometimes toxic inorganic oxidants that are less favourable from an environmental and economical point of view. In contrast to such processes, catalytic epoxidation processes employing H2O2 oxidant are preferred for green processing. Herein is reported a highly efficient green process for the epoxidation of olefins using H2O2 oxidant and modified silver polyoxometalate catalysts at 65°C. The preparation and activity of the catalysts are described. The method enjoys >90% conversion and ≥99% selectivity to the epoxide for a variety of cyclic and linear olefins including terminal ones. The catalysts are easily recovered by filtration and are reusable several times. Key words: Epoxidation, olefins, hydrogen peroxide, polyoxometalate, silver catalysts. INTRODUCTION The catalytic epoxidation of olefins is very important in compared to organic peroxides and peracids (Jones, the chemical industry since epoxides are versatile and 1999; Lane and Burgess, 2003). -
Part I. the Total Synthesis Of
AN ABSTRACT OF THE THESIS OF Lester Percy Joseph Burton forthe degree of Doctor of Philosophy in Chemistry presentedon March 20, 1981. Title: Part 1 - The Total Synthesis of (±)-Cinnamodialand Related Drimane Sesquiterpenes Part 2 - Photochemical Activation ofthe Carboxyl Group Via NAcy1-2-thionothiazolidines Abstract approved: Redacted for privacy DT. James D. White Part I A total synthesis of the insect antifeedant(±)-cinnamodial ( ) and of the related drimanesesquiterpenes (±)-isodrimenin (67) and (±)-fragrolide (72)are described from the diene diester 49. Hydro- boration of 49 provided the C-6oxygenation and the trans ring junction in the form of alcohol 61. To confirm the stereoselectivity of the hydroboration, 61 was convertedto both (t)-isodrimenin (67) and (±)-fragrolide (72) in 3 steps. A diisobutylaluminum hydride reduction of 61 followed by a pyridiniumchlorochromate oxidation and treatment with lead tetraacetate yielded the dihydrodiacetoxyfuran102. The base induced elimination of acetic acid preceded theepoxidation and provided 106 which contains the desired hydroxy dialdehydefunctionality of cinnamodial in a protected form. The epoxide 106 was opened with methanol to yield the acetal 112. Reduction, hydrolysis and acetylation of 112 yielded (t)- cinnamodial in 19% overall yield. Part II - Various N- acyl- 2- thionothiazolidineswere prepared and photo- lysed in the presence of ethanol to provide the corresponding ethyl esters. The photochemical activation of the carboxyl function via these derivatives appears, for practical purposes, to be restricted tocases where a-keto hydrogen abstraction and subsequent ketene formation is favored by acyl substitution. Part 1 The Total Synthesis of (±)-Cinnamodial and Related Drimane Sesquiterpenes. Part 2 Photochemical Activation of the Carboxyl Group via N-Acy1-2-thionothiazolidines. -
Course Material 2.Pdf
Reactive Intermediates Source: https://www.askiitians.com/iit-jee-chemistry/organic-chemistry/iupac- and-goc/reaction-intermediates/ Table of Content • Carbocations • Carbanions • Free Radicals • Carbenes • Arenium Ions • Benzynes Synthetic intermediate are stable products which are prepared, isolated and purified and subsequently used as starting materials in a synthetic sequence. Reactive intermediate, on the other hand, are short lived and their importance lies in the assignment of reaction mechanisms on the pathway from the starting substrate to stable products. These reactive intermediates are not isolated, but are detected by spectroscopic methods, or trapped chemically or their presence is confirmed by indirect evidence. • Carbocations Carbocations are the key intermediates in several reactions and particularly in nucleophilic substitution reactions. Structure of Carbocations : Generally, in the carbocations the positively charged carbon atom is bonded to three other atoms and has no nonbonding electrons. It is sp 2 hybridized with a planar structure and bond angles of about 120°. There is a + vacant unhybridized p orbital which in the case of CH 3 lies perpendicular to the plane of C—H bonds. Stability of Carbocations: There is an increase in carbocation stability with additional alkyl substitution. Thus one finds that addition of HX to three typical olefins decreases in the order (CH 3)2C=CH 2>CH 3—CH = CH 2 > CH 2 = CH 2. This is due to the relative stabilities of the carbocations formed in the rate determining step which in turn follows from the fact that the stability is increased by the electron releasing methyl group (+I), three such groups being more effective than two, and two more effective than one. -
Reactions of Benzene & Its Derivatives
Organic Lecture Series ReactionsReactions ofof BenzeneBenzene && ItsIts DerivativesDerivatives Chapter 22 1 Organic Lecture Series Reactions of Benzene The most characteristic reaction of aromatic compounds is substitution at a ring carbon: Halogenation: FeCl3 H + Cl2 Cl + HCl Chlorobenzene Nitration: H2 SO4 HNO+ HNO3 2 + H2 O Nitrobenzene 2 Organic Lecture Series Reactions of Benzene Sulfonation: H 2 SO4 HSO+ SO3 3 H Benzenesulfonic acid Alkylation: AlX3 H + RX R + HX An alkylbenzene Acylation: O O AlX H + RCX 3 CR + HX An acylbenzene 3 Organic Lecture Series Carbon-Carbon Bond Formations: R RCl AlCl3 Arenes Alkylbenzenes 4 Organic Lecture Series Electrophilic Aromatic Substitution • Electrophilic aromatic substitution: a reaction in which a hydrogen atom of an aromatic ring is replaced by an electrophile H E + + + E + H • In this section: – several common types of electrophiles – how each is generated – the mechanism by which each replaces hydrogen 5 Organic Lecture Series EAS: General Mechanism • A general mechanism slow, rate + determining H Step 1: H + E+ E El e ctro - Resonance-stabilized phile cation intermediate + H fast Step 2: E + H+ E • Key question: What is the electrophile and how is it generated? 6 Organic Lecture Series + + 7 Organic Lecture Series Chlorination Step 1: formation of a chloronium ion Cl Cl + + - - Cl Cl+ Fe Cl Cl Cl Fe Cl Cl Fe Cl4 Cl Cl Chlorine Ferric chloride A molecular complex An ion pair (a Lewis (a Lewis with a positive charge containing a base) acid) on ch lorine ch loronium ion Step 2: attack of -
Lecture Outline a Closer Look at Carbocation Stabilities and SN1/E1 Reaction Rates We Learned That an Important Factor in the SN
Lecture outline A closer look at carbocation stabilities and SN1/E1 reaction rates We learned that an important factor in the SN1/E1 reaction pathway is the stability of the carbocation intermediate. The more stable the carbocation, the faster the reaction. But how do we know anything about the stabilities of carbocations? After all, they are very unstable, high-energy species that can't be observed directly under ordinary reaction conditions. In protic solvents, carbocations typically survive only for picoseconds (1 ps - 10–12s). Much of what we know (or assume we know) about carbocation stabilities comes from measurements of the rates of reactions that form them, like the ionization of an alkyl halide in a polar solvent. The key to connecting reaction rates (kinetics) with the stability of high-energy intermediates (thermodynamics) is the Hammond postulate. The Hammond postulate says that if two consecutive structures on a reaction coordinate are similar in energy, they are also similar in structure. For example, in the SN1/E1 reactions, we know that the carbocation intermediate is much higher in energy than the alkyl halide reactant, so the transition state for the ionization step must lie closer in energy to the carbocation than the alkyl halide. The Hammond postulate says that the transition state should therefore resemble the carbocation in structure. So factors that stabilize the carbocation also stabilize the transition state leading to it. Here are two examples of rxn coordinate diagrams for the ionization step that are reasonable and unreasonable according to the Hammond postulate. We use the Hammond postulate frequently in making assumptions about the nature of transition states and how reaction rates should be influenced by structural features in the reactants or products. -
Spectroscopic and Photophysical Properties of the Trioxatriangulenium Carbocation and Its Interactions with Supramolecular Systems
View metadata,Downloaded citation and from similar orbit.dtu.dk papers on:at core.ac.uk May 03, 2019 brought to you by CORE provided by Online Research Database In Technology Spectroscopic and Photophysical Properties of the Trioxatriangulenium Carbocation and its Interactions with Supramolecular Systems Reynisson, Johannes Publication date: 2000 Document Version Publisher's PDF, also known as Version of record Link back to DTU Orbit Citation (APA): Reynisson, J. (2000). Spectroscopic and Photophysical Properties of the Trioxatriangulenium Carbocation and its Interactions with Supramolecular Systems. Roskilde: Risø National Laboratory. Denmark. Forskningscenter Risoe. Risoe-R, No. 1191(EN) General rights Copyright and moral rights for the publications made accessible in the public portal are retained by the authors and/or other copyright owners and it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights. Users may download and print one copy of any publication from the public portal for the purpose of private study or research. You may not further distribute the material or use it for any profit-making activity or commercial gain You may freely distribute the URL identifying the publication in the public portal If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim. Spectroscopic and Photophysical Properties of the Trioxatriangulenium Carbocation and its Interactions with Supramolecular Systems Jóhannes Reynisson OO O Risø National Laboratory, Roskilde, Denmark June 2000 1 Abstract Trioxatriangulenium (TOTA+, 4,8,12-trioxa-4,8,12,12c-tetrahydro- dibenzo[cd,mn]-pyrenylium) is a closed shell carbocation which is stable in its crystalline form and in polar solvents at ambient temperatures. -
Epoxidation of Olefins Using Molecular Oxygen
Epoxidation of Olefins Using Molecular Oxygen Zhongxing Huang Sep 16th, 2015 1 Major Challenge in Catalysis Key points . Low temperature . Selective May 31st, 1993, C&EN News. 2 Most Ancient Chemistry-Oxygenase Monooxygenase catalyzes the incorporation of one atom of oxygen into the product Iron-Containing Enzymes, RSC Publishing, 2011. 3 Most Ancient Chemistry-Oxygenase Dioxygenase incorporates both oxygen atoms into the product Shen, B.; Gould, S. J. Biochemistry 1991, 30, 8936. Gould, S. J.; Kirchmeier, M. J.; LaFever, R. E. J. Am. Chem. Soc. 1996, 118, 7663. 4 Most Ancient Chemistry-Oxygenase Monooxygenase catalyzes the incorporation of one atom of oxygen into the product . Ideal system should avoid use of reductants Dioxygenase incorporates both oxygen atoms into the product 5 Most Ancient Chemistry-Oxygenase Monooxygenase catalyzes the incorporation of one atom of oxygen into the product . Ideal system should avoid use of reductants Dioxygenase incorporates both oxygen atoms into the product Ideal Dioxygenase incorporates both oxygen atoms into the epoxide 6 Most Ancient Chemistry-Oxygenase Monooxygenase catalyzes the incorporation of one atom of oxygen into the product . Ideal system should avoid use of reductants Dioxygenase incorporates both oxygen atoms into the product Ideal Dioxygenase incorporates both oxygen atoms into the epoxide 7 Industrial Process- EO and PO . Top chemicals produced in US (2004,103 ton) 1 sulfuric acid 35954 2 nitrogen 30543 3 ethylene 25682 4 oxygen 25568 5 propylene 15345 6 chlorine 12166 7 ethylene dichloride 12163 8 phosphoric acid 11463 9 ammonia 10762 10 sodium hydroxide 9508 11 benzene 7675 12 nitric acid 6703 13 ammonium nitrate 6021 14 ethylbenzene 5779 15 urea 5755 16 styrene 5394 17 hydrochloric acid 5012 18 ethylene oxide 3772 19 cumene 3736 20 ammonium sulfate 2643 8 Industrial Process- EO and PO . -
Nonclassical Carbocations: from Controversy to Convention
Nonclassical Carbocations H H C From Controversy to Convention H H H A Stoltz Group Literature Meeting brought to you by Chris Gilmore June 26, 2006 8 PM 147 Noyes Outline 1. Introduction 2. The Nonclassical Carbocation Controversy - Winstein, Brown, and the Great Debate - George Olah and ending the discussion - Important nonclassical carbocations 3. The Nature of the Nonclassical Carbocation - The 3-center, 2-electron bond - Cleaving C-C and C-H σ−bonds - Intermediate or Transition state? Changing the way we think about carbocations 4. Carbocations, nonclassical intermediates, and synthetic chemistry - Biosynthetic Pathways - Steroids, by W.S. Johnson - Corey's foray into carbocationic cascades - Interesting rearrangements - Overman and the Prins-Pinacol Carbocations: An Introduction Traditional carbocation is a low-valent, trisubstituted electron-deficient carbon center: R superacid R R LG R R R R R R "carbenium LGH ion" - 6 valence e- - planar structure - empty p orbital Modes of stabilization: Heteroatomic Assistance π-bond Resonance σ-bond Participation R X H2C X Allylic Lone Pair Anchimeric Homoconjugation Hyperconjugation Non-Classical Resonance Assistance Stabilization Interaction Outline 1. Introduction 2. The Nonclassical Carbocation Controversy - Winstein, Brown, and the Great Debate - George Olah and ending the discussion - Important nonclassical carbocations 3. The Nature of the Nonclassical Carbocation - The 3-center, 2-electron bond - Cleaving C-C and C-H σ−bonds - Intermediate or Transition state? Changing the way we think about carbocations 4. Carbocations, nonclassical intermediates, and synthetic chemistry - Biosynthetic Pathways - Steroids, by W.S. Johnson - Corey's foray into carbocationic cascades - Interesting rearrangements - Overman and the Prins-Pinacol The Nonclassical Problem: Early Curiosities Wagner, 1899: 1,2 shift OH H - H+ Meerwein, 1922: 1,2 shift OH Meerwin, H. -
Reactions of Aromatic Compounds Just Like an Alkene, Benzene Has Clouds of Electrons Above and Below Its Sigma Bond Framework
Reactions of Aromatic Compounds Just like an alkene, benzene has clouds of electrons above and below its sigma bond framework. Although the electrons are in a stable aromatic system, they are still available for reaction with strong electrophiles. This generates a carbocation which is resonance stabilized (but not aromatic). This cation is called a sigma complex because the electrophile is joined to the benzene ring through a new sigma bond. The sigma complex (also called an arenium ion) is not aromatic since it contains an sp3 carbon (which disrupts the required loop of p orbitals). Ch17 Reactions of Aromatic Compounds (landscape).docx Page1 The loss of aromaticity required to form the sigma complex explains the highly endothermic nature of the first step. (That is why we require strong electrophiles for reaction). The sigma complex wishes to regain its aromaticity, and it may do so by either a reversal of the first step (i.e. regenerate the starting material) or by loss of the proton on the sp3 carbon (leading to a substitution product). When a reaction proceeds this way, it is electrophilic aromatic substitution. There are a wide variety of electrophiles that can be introduced into a benzene ring in this way, and so electrophilic aromatic substitution is a very important method for the synthesis of substituted aromatic compounds. Ch17 Reactions of Aromatic Compounds (landscape).docx Page2 Bromination of Benzene Bromination follows the same general mechanism for the electrophilic aromatic substitution (EAS). Bromine itself is not electrophilic enough to react with benzene. But the addition of a strong Lewis acid (electron pair acceptor), such as FeBr3, catalyses the reaction, and leads to the substitution product.