Download or read book Total Synthesis of Pseudo dimeric Cyclobutane Natural Products Via Br nsted Acid catalyzed Asymmetric 2 2 Photocycloadditions written by Matthew James Genzink and published by . This book was released on 2023 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: Pseudo-dimeric cyclobutanes constitute a large class of natural products. Though a [2+2] cycloaddition would be the most direct way to access these molecules, its use in total synthesis has been limited due to selectivity challenges in the cycloaddition. The work in this dissertation details the development of a new platform for enantioselective [2+2] photocycloadditions based on chiral Brønsted acid catalysis and its application to the total synthesis of (pseudo)-dimeric cyclobutane natural products. Initial mechanistic investigations revealed that the reaction proceeds via a chromophore activation mechanism in which coordination of the catalyst to the substrate engenders a red-shifted substrate absorption. This insight enabled the development of (hetero)dimerization reactions, the products of which could be transformed into enantioenriched natural products.
Download or read book Synthesis of Cyclobutane Natural Products Using C H Functionalization Logic written by Will Ryan Gutekunst and published by . This book was released on 2013 with total page 668 pages. Available in PDF, EPUB and Kindle. Book excerpt: C-H functionalization logic is rapidly permeating the way organic chemists approach synthesis and deconstruct targets molecules. With methodological advances developing at an increasing pace, new disconnections and strategies once thought impossible are now available for consideration during synthesis planning. While these methods have sporadically been utilized to great effect for decades, only recently have these strategies been formalized and articulated as an efficient and effective means to construct molecules of interest. When compared to traditional prefunctionalization approaches, there are inherent benefits to using C-H bonds as latent functional groups in terms of redox, atom and step economy. This thesis begins with an overview of historical examples that exemplify the tenets of C-H functionalization logic, including specific case studies from our own lab. The following chapters outline the design and execution of this strategy to pseudodimeric cyclobutane natural products as an alternative to [2+2] photocycloaddition. Throughout all of the projects, methodological and strategic innovations were critical for success. During the studies toward dictazole A, a diastereoselective synthesis of 1,1- cyclobutanedicarboxylates was devised and an easily cleavable directing group for C-H functionalization was created. En route to piperarborenines, a one-pot synthesis of 1,3- cyclobutanedicarboxylates was invented and the structure of piperarborenine D was revised using sequential sp 3 C-H cross coupling reactions. The synthesis of the proposed structure of pipercyclobutanamide A resulted in the first sp 3 C-H olefination on a cyclobutane, a new method to access all- cis -cyclobutanes and the direct conversion of an aminoquinoline amide to an aldehyde.
Download or read book Part I Synthesis of Naturally Occurring Cyclobutanes Via Stereoselective Photocycloadditions Part II Development of Photocatalytic Net oxidative Transformations Using Copper II Salts as Terminal Oxidants written by Byung Joo Lee (Ph.D.) and published by . This book was released on 2020 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: Among many unique transformations accessible using photochemical activation, the [2+2] photocycloaddition of olefins has had the largest impact on total synthesis. However, relatively few asymmetric total syntheses of natural products involving an enantioselective [2+2] photocycloaddition have been reported to date. This is due in part to the difficulty of conducting enantioselective [2+2] photocycloaddition reactions. Recent work in the Yoon lab has focused on developing enantioselective [2+2] photocycloadditions using a dual catalysis approach. The work presented herein will describe the use of chiral Lewis acid catalysts to enable highly enantioselective photocycloadditions and further application of this strategy toward natural product synthesis. Photoredox catalysis is a powerful strategy to generate radical and radical ion intermediates under exceptionally mild conditions. However, the development of photocatalytic oxidation reactions has been much more challenging compared to redox-neutral and net reductive transformations due to the lack of generally applicable terminal oxidants that are compatible with photoredox conditions. This thesis describes the use of copper(II) salts as terminal oxidants for robust photocatalytic oxidation reactions.
Download or read book Natural Product Synthesis Via Cyclobutanes written by Jungchul Kim and published by . This book was released on 2000 with total page 492 pages. Available in PDF, EPUB and Kindle. Book excerpt: PART I. Asymmetric syntheses of both natural (+)- and nonnatural ( - )- byssochlamic acid via a [2+2] photoaddition-cycloreversion strategy are described. X-ray crystallographic analysis of the cyclohexylamine salt 99 showed that the structure of the monomethyl ester 100 from esterase hydrolysis of 44 was originally misassigned as 56. The enantiomeric relationship of the two diolides 106 and 70 permitted syntheses of nonnatural byssochlamic acid ( - )-3 and natural byssochiamic acid (+)-3 from enantiopure alcohol (+)-64 and from its enantiomer ( - )-110, respectively. Through the use of (±)-103 to reach both enantiomers of byssochlamic acid (3) and subsequent epimerization of the npropyl chain, it was proved that the cis configuration of the two alkyl substituents is strongly preferred in the natural product. PART II. An asymmetric approach towards the nootropic agent huperzine A is described. Formation of cyclobutane 122 with the desired stereochemistry was accomplished using intramolecular [2+2] photoaddition of the enantiopure enone 121. Attempts to prepare the methoxypyridine system via an azadiene Diels- Alder reaction were unsuccessful. However, intramolecular Michael addition of 181 produced silyl ether 182 which was converted into the pyridone 187 by treatment with hydrogen fluoride followed by selenoxide elimination. Attempts to effect the key sigmatropic rearrangement of ketone 197 into a direct precursor of huperzine A were unsuccessful.
Download or read book 2 2 Photocycloaddition in Natural Product Synthesis written by Roel Klein Nijenhuis and published by . This book was released on 2018 with total page 229 pages. Available in PDF, EPUB and Kindle. Book excerpt: [2+2]-Photocycloaddition is a powerful method to synthesise highly strained, complex and multicyclic compounds. The research described in this thesis focusses on using this reaction to pursue the total synthesis of a number of complex natural products. The main project focusses on the synthesis of solanoeclepin A, an extremely potent hatching agent of the potato cyst nematode. To reach this goal, the molecule was divided in two parts, the left- and the right-hand substructure. With the left-hand substructure completed in previous research, the goal was now to synthesise the right-hand substructure, and to complete the total synthesis by connecting the two fragments. The key step is a [2+2]-photocycloaddition of 2-substituted 3-methyl-2-cyclohexenones, described in chapter 3. Using this reaction the highly strained bicyclo[2.1.1]cyclohexane core structure of the natural product was accessed from simple starting materials in a few steps. A racemic approach to the right-hand substructure of solanoeclepin A is described in chapter 2. Extensive research ultimately led to a short and efficient enantioselective formal synthesis of solanoeclepin A, as described in chapter 4. Finally, the efforts to combine both fragments are described in chapter 5. The final chapter describes the first total syntheses of aquatolide and wilfolide B. Aquatolide was prepared using the [2+2]-photocycloaddition of an allene-substituted pentenolide, ultimately leading to the natural product. Retro-ene type rearrangement of the cycloaddition product led to a different carbon skeleton, leading to the successful total synthesis of wilfolide B.
Download or read book The Art of Writing Reasonable Organic Reaction Mechanisms written by Robert B. Grossman and published by Springer Science & Business Media. This book was released on 2007-07-31 with total page 371 pages. Available in PDF, EPUB and Kindle. Book excerpt: Intended for students of intermediate organic chemistry, this text shows how to write a reasonable mechanism for an organic chemical transformation. The discussion is organized by types of mechanisms and the conditions under which the reaction is executed, rather than by the overall reaction as is the case in most textbooks. Each chapter discusses common mechanistic pathways and suggests practical tips for drawing them. Worked problems are included in the discussion of each mechanism, and "common error alerts" are scattered throughout the text to warn readers about pitfalls and misconceptions that bedevil students. Each chapter is capped by a large problem set.
Download or read book Shining Light on Cyclobutane Synthesis written by Alec Hopper Waters and published by . This book was released on 2019 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: Cyclobutane rings can be found in many different natural and artificial small molecules but the high ring strain associated the 4-membered ring makes their preparation difficult. Most commonly, cyclobutanes are formed through the [2+2] cycloaddition of two alkenes, which is forbidden under thermal conditions, but is photochemically allowed. UV light catalyzed reactions have several drawbacks including the production of unwanted side products and potential decomposition of desired products. This work reports the use of an iridium transition metal catalyst to promote [2+2] cycloadditions of vinylogous ester compounds under lower energy visible light. These reactions offer modest yields and excellent regio- and diastereoselectivity. Absorption and phosphorescence data are reported for targeted substrates, reagents, catalysts, and additives to help elucidate the mechanism of these cycloadditions, which is believed to proceed via triplet energy transfer from the metal catalyst to a conjugate organic substrate.
Download or read book Total Synthesis of Cyanthiwigin Natural Products Via Double Asymmetric Catalytic Alkylation and Investigations Into the Nature of Double Asymmetric written by John Andrew Enquist and published by . This book was released on 2011 with total page 592 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Total Synthesis of Beauvericin Using Dehydroamino Acid Residues to Facilitate Cyclization written by Gregory Thomas Cizio and published by . This book was released on 2014 with total page 101 pages. Available in PDF, EPUB and Kindle. Book excerpt: A unique strategy that helps facilitate macrocyclization has been developed and utilized in the synthesis of a cyclic hexadepsipeptide natural product. By using dehydrophenylalanine amino acids in the synthesis of beauvericin, the precursor to the macrocycle is folded in such a way that the C- and the N- termini of the depsipeptide are closer together and cyclization is facilitated. Two strategies towards construction of the macrocycle have been investigated: (1) a cyclotrimerization approach which utilizes a monomeric dipeptide oxazolone and (2) a linear approach which cyclizes a hexadepsipeptide oxazolone. The macrocycle then underwent a global N-methylation followed by rhodium-catalyzed asymmetric hydrogenation which reduced the unsaturated amino acid residues to their desired saturated forms to give rise to the natural product. With the cyclotrimerization route, beauvericin was afforded in 10% yield over 8 steps, and with the linear route, beauvericin was afforded in 19% yield over 12 steps.
Download or read book Toward a Visible Light Mediated 2 2 Photocycloaddition cyclobutane Fragmentation Synthesis of Natural Products written by Jeffrey Rein and published by . This book was released on 2021 with total page 246 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Toxicology written by C. P. Stewart and published by Elsevier. This book was released on 2013-10-22 with total page 938 pages. Available in PDF, EPUB and Kindle. Book excerpt: Toxicology: Mechanisms and Analytical Methods, Volume II provides an account of the general methods of chemical analysis available to the toxicologist, discussion of the principles on which they are based, and a survey of the material to which they are applied. The volume supplements the methods presented in the first volume. It provides specific examples of general procedures; considers the important groups of poisons; arranges the order of extraction from biological material; and discusses the methods for identifying and determining the members of each poison group. The book will be invaluable to toxicologists, clinical chemists, and biochemists.
Download or read book Organic Reaction Mechanisms written by Michael Edenborough and published by CRC Press. This book was released on 2017-12-21 with total page 508 pages. Available in PDF, EPUB and Kindle. Book excerpt: This text is designed to teach students how to write organic reaction mechanisms. It starts from the absolute basics - counting the numbers of electrons around a simple atom. Then, in small steps, the text progresses to advanced mechanisms. the end, all the major mechanistic routes have been covered. The text is in the form of interactive sections, which are designed to facilitate the assimilation of the information conveyed, so that by the end the student should already know the contents without the need for extensive revision.
Download or read book Mechanism and Theory in Organic Chemistry written by Thomas H. Lowry and published by HarperCollins Publishers. This book was released on 1987 with total page 1110 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Pushing Electrons written by Weeks and published by . This book was released on 2013 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Soybean Seed Composition written by Moulay Abdelmajid Kassem and published by Springer Nature. This book was released on 2022-01-10 with total page 638 pages. Available in PDF, EPUB and Kindle. Book excerpt: Soybean Seed Composition covers three decades of advances in quantitative trait loci (QTL) mapping of seed protein, oil, fatty acids, amino acids, sugars, mineral nutrients, isoflavones, lunasin, and other beneficial compounds. It opens with coverage of seed protein, oil, fatty acids, and amino acids and the effects that genetic and environmental factors have on them. Detailed discussion of QTL that control seed protein, oil, and fatty acids follows, and the book also covers seed amino acids, macronutrients, micronutrients, sugars, and other compounds that are key to selection for crop improvement. The book also provides an overview of two decades of QTL mapping of mineral deficiencies in soybean, which sheds light on the importance of a balanced mineral nutrition in soybean and other crops, elucidates salt stress tolerance QTL mapping, which is another challenge that faces soybean and other crop production worldwide. The importance of soybean seed isoflavones from their biosynthesis and quantification methods to locations and variations in seeds, roots, and leaves, to their QTL mapping is discussed, as well as providing key information on lunasin, a bioactive anticancer peptide in soybean seeds that will help farmers and breeders to develop soybean cultivars with improved seed isoflavones and lunasin content. The book will be of interest to graduate students, academics, and researchers in the fields of genetic and QTL mapping of important agronomic traits in soybean and other crops.
Download or read book Electron Flow in Organic Chemistry written by Paul H. Scudder and published by John Wiley & Sons, Incorporated. This book was released on 1992-02-20 with total page 392 pages. Available in PDF, EPUB and Kindle. Book excerpt: With the goal of helping students develop a good intuition for organic chemistry, it approaches the material from a mechanistic viewpoint. Presents twenty electron flow pathways as the building blocks of all the common mechanistic processes. Thus, students deal with a smaller number of reactant classes instead of studying each reaction as a separate case. Uses physical models such as energy surfaces to aid the decision-making process; includes a unique chapter that teaches students how to make a multivariable decision; and contains advanced explanations using interaction diagrams and molecular orbital theory.
