DOCSLIB.ORG

Unveiling Potent Photooxidation Behavior of Catalytic Photoreductants Karina Targos,‡ Oliver P

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Unveiling Potent Photooxidation Behavior of Catalytic Photoreductants Karina Targos,‡ Oliver P Unveiling Potent Photooxidation Behavior of Catalytic Photoreductants Karina Targos,‡ Oliver P. Williams,‡ and Zachary K. Wickens* Department of Chemistry, University of Wisconsin–Madison, Madison, Wisconsin 53706, United States. Supporting Information Placeholder 4 ABSTRACT: We describe a photocatalytic system that intersystem crossing. Despite tremendous effort in 4,5 reveals latent photooxidant behavior from one of the most photoredox catalyst design, excited state potentials reducing conventional photoredox catalysts, N- beyond roughly –2 and +2 V vs SCE remain difficult to 6 phenylphenothiazine (PTH). This aerobic photochemical achieve using conventional photocatalysis (Figure 1A). reaction engages difficult to oxidize feedstocks, such as Unfortunately, this redox window excludes numerous benzene, in C(sp2)–N coupling reactions through direct abundant hydrocarbon feedstocks from facile 7 oxidation. Mechanistic studies are consistent with activation photoinduced electron transfer. of PTH via photooxidation and that Lewis acid co-catalysts To overcome the energetic limitations intrinsic to scavenge inhibitors formed upon catalyst activation. conventional photoredox catalysis, König and coworkers recently designed a photocatalytic system that drives challenging reductive SET events using the energy of two photons rather than one. This consecutive photoninduced Reactions driven by single electron transfer (SET) are electron transfer (conPET)8 strategy relies on a catalytic pervasive in organic chemistry. Consequently, new photooxidant and sacrificial reductant that, upon strategies to induce redox events are poised to profoundly irradiation, result in a potent radical anion photoreductant impact synthetic chemistry.1 Photoredox catalysis has (Figure 1B). Despite its mechanistic complexity, this unlocked a broad range of attractive new transformations approach is practical and operationally simple; it leverages through conversion of energy from readily accessible LEDs inexpensive and safe LEDs to accomplish reactions that into chemical redox potential.2 However, only a portion of otherwise require UV photoreactors or harsh chemical this energy3 can be harnessed due to inevitable energy reductants. Following proof-of-concept aryl halide losses from vibrational relaxation, internal conversion, and reductions,8,9 this approach has enabled photochemical Table 1. Survey of oxidants and photoreductants.a–d CO2Et alternatives to alkali metal reductants in reactions such as CO2Et 10 11 [catalyst] Birch reductions and sulfonamide cleavage. + N HN N N LED irradiation In contrast to the progress in photoreductions, 1 [oxidant] 2 oxidations driven by the consumption of multiple photons have remained elusive. We suspect that this is the 100 Ar2 consequence of two inextricable challenges: (1) the N N N catalyst must be a competent photocatalyst in both the 75 S Ar1 O Ar1 N 2a,8b closed shell and radical cation states and (2) the Ar2 PTH PC-1 PC-2 terminal oxidant must efficiently activate the catalyst but 50 not otherwise interfere with the reaction (Figure 1C).12 yield (%) Given the difficulty applying multiple photons towards a 25 challenging SET oxidation, photoredox reactions initiated by SET oxidation are typically limited to electron-rich 0 13 PhI PhBr CH NOPFO O PhI PhBr CH NOPFO O PhI PhBr CH NOPFO O hydrocarbon substrates. 2 2 d 2 2 d 2 2 d 2 Br 2 Br 2 Br Our group is investigating diverse strategies to expand 2 6 2 6 2 6 a 14 Reactions were conducted on a 0.05 mmol scale in 1:1 MeCN:PhH for the redox potentials accessible via photoredox catalysis. 1 24h, unless noted otherwise, using 2 equiv oxidant or 1 atm O2. Ar = 4- We questioned whether conventional photoreductants, biphenyl. Ar2 = 2-napthyl. bPTH irradiated using 390 nm Kessil lamp. cPC- 1 and PC-2 irradiated using Tuna Blue Kessil lamp. d1:1 TFE:PhH. which typically possess persistent radical cation states, radical cation without additional energy from light, could be repurposed as strong photooxidants using a 24 NOPF6, provided low yield of benzene oxidation conPET strategy.15 We hypothesized photochemical products using all three catalysts. However, under one conditions designed to drive these photocatalysts towards atmosphere of O2, PTH promoted oxidative coupling in their oxidized congeners could reveal oxidation behavior. promising yield (14%). Given the enhanced stability of To probe this hypothesis, we targeted cyclic triarylamine radical cations in fluorinated alcohol solvents,25 we photoreductants. These are a well-established and modular substituted MeCN for trifluoroethanol (TFE). This family of neutral photoreductants6d,16 and isolated reports resulted in a modest increase in reaction yield with PTH suggest their radical cation congeners could exhibit but only traces of product with the other two catalysts. Of photochemical activity.17 We selected the Nicewicz-type13e note, while most photoredox catalysts undergo rapid oxidative coupling of arenes and N-heterocyclic intersystem crossing to a long-lived triplet,2a,5c PTH is a nucleophiles as a model reaction. This synthetically singlet excited state reductant.26 This property circumvents valuable transformation is representative of the general photocatalyst deactivation by triplet-triplet annihilation challenges in oxidative photoredox catalysis; it has been with O2. predominantly limited to electron-rich arene substrates, such as anisole derivatives.18 Difficult to oxidize arene We suspected that BET between PTH radical cation and 27 substrates, such as benzene, mandate high energy UV light superoxide might attenuate reactivity under these 28 (UVB or shorter),6a strong ground state oxidants (e.g. conditions (Figure 2). Indeed, when synthetically prepared DDQ) that absorb visible light,19 or more technically PTH radical cation is treated with KO2, we observe a rapid 1 complex electrophotocatalytic approaches.20,21 Thus, color change and reformation of PTH by H-NMR. Given beyond providing a proof-of-concept, we envisioned that that superoxide generation is inextricable from aerobic promoting this transformation using a stable photocatalyst with only inexpensive LEDs would be a synthetically useful complement to existing methods. First, we examined three distinct photoreductants6d,22 and a range of oxidants for activity in the oxidative coupling 23 of benzene (Eox = 2.5 V vs. SCE) and pyrazole 1 (Table 1). We initially aimed to generate the catalyst radical cation congener via photoreduction of reagents that undergo irreversible decomposition after SET to avoid catalyst deactivation via back electron transfer (BET). Excitingly, these data revealed that N-phenylphenothiazine (PTH), the most reducing photocatalyst of the series, could promote this challenging oxidative coupling in low yield using organohalides as the oxidant. A sufficiently strong oxidant to oxidize each catalyst to the corresponding 2 catalyst activation, this observation could account for the of the additive, suggesting a co-catalytic role for LiClO4 rather modest reactivity of this catalytic system (Table 2, entry 1). than it purely sequestrating stoichiometric byproducts (entry As expected, addition of 5 mol % KO2 to the reaction mixture 4). In principle, the lithium co-catalyst could mitigate BET by completely suppressed product formation (entry 2). We promoting superoxide disproportionation.29 Consistent with hypothesized that additives capable of sequestering or this proposed Lewis acidic role, alkylammonium salts had no scavenging this inhibitor would enhance the observed impact on the reaction (entry 5); whereas, other Lewis acidic reactivity. Guided by this model, we found addition of one lithium salts retained the catalytic effect (entries 6 and 7). equivalent of an inexpensive, redox innocent Lewis acid, Final tuning of the reaction parameters revealed adjusting the LiClO4, dramatically improved the yield of oxidative coupling solvent mixture to include a small amount of product (entry 3). Reduction of the LiClO4 loading to a hexafluoroisopropanol (HFIP) delivered the desired product substoichiometric quantity (20 mol %) retained the benefits in 89% yield (entry 8). Substitution of PTH with other Table 2. Reaction optimizationa triarylamine photoreductants or a classic metal-based CO2Et CO2Et PTH (5 mol %) photoreductant, Ir(ppy)3, resulted in only trace yield of [additive] + N oxidation product under these otherwise optimal conditions HN N N 390 nm LED (entries 9–11). 1 O2 (1 atm) 2 Having identified a promising catalytic system, we entry additive yield (%) examined the scope of this new process (Table 3). Pyrazole 1 none 31 nucleophiles bearing a range of electron-withdrawing 2 KO2 (5 mol %) <2 moieties, including ketones (3), aldehydes (4), nitriles (5), 3 LiClO4 (1 equiv) 86 and trifluoromethyl groups (6) were oxidatively coupled to 4 LiClO4 (20 mol %) 73 benzene. Halogenated pyrazoles (7 and 8) were also 5 n-Bu4ClO4 (20 mol %) 29 productively coupled despite the fact that PTH is a potent 6 LiPF6 (20 mol %) 64 photoreductant. Prior approaches capable of oxidizing 7 LiOTf (20 mol %) 56 benzene have not been readily amenable to the arylation of b 30 8 LiClO4 (20 mol %) 89 neutral heterocyclic substrates. In contrast, we observed b,c 9 PC-1 (5 mol %), LiClO4 (20 mol %) <2 coupling of both parent pyrazole (9) and even an electron- b,c 10 PC-2 (5 mol %), LiClO4 (20 mol %) <2 rich analog (10), albeit in diminished yield relative to the b,c 11 Ir(ppy)3 (1 mol %), LiClO4 (20 mol %) <2 electron deficient heterocyclic coupling partners.
Load more

Recommended publications
  • Curriculum Vitae Kazimer Lennon Skubi
    CURRICULUM VITAE KAZIMER LENNON SKUBI Skidmore College Department of Chemistry Office: (518) 580-5147 815 North Broadway Email: [email protected] Saratoga Springs, NY 12866 ORCID: 0000-0002-9689-1842 EDUCATION AND TRAINING Yale University 2017–2020 NIH F32 Postdoctoral Fellow (Advisor: Patrick Holland) University of Wisconsin–Madison 2011–2017 Ph.D. in Chemistry (Advisor: Tehshik Yoon) Thesis Title: “New Strategies for Catalytic Stereocontrol in Photochemical Synthesis” Carleton College 2007–2011 B.A. in Chemistry, summa cum laude ACS-Certified Degree, Distinction in Major, Distinction in Senior Integrative Exercise PROFESSIONAL EXPERIENCE Visiting Assistant Professor of Chemistry, Skidmore College, Saratoga Springs, NY 2020–present NIH F32 Postdoctoral Fellow, Yale University, New Haven, CT 2018–2020 Postdoctoral Associate, Yale University, New Haven, CT 2017–2018 Graduate Student Research Assistant, University of Wisconsin–Madison, Madison, WI 2015–2017 Graduate Student Teaching Assistant, University of Wisconsin–Madison, Madison, WI 2011–2015 TEACHING EXPERIENCE Skidmore College CH 125: Principles of Chemistry + Lab Fall 2020 University of Wisconsin–Madison (Teaching Assistant) CHEM 344: Organic Chemistry Laboratory Fall 2011, Spring 2012 CHEM 345: Organic Chemistry II Spring 2014 CHEM 346: Intermediate Organic Chemistry Laboratory Fall 2013, Fall 2014, Fall 2015 CHEM 636: Introduction to NMR Fall 2012, Spring 2013 CHEM 637: Advanced Methods in NMR Summer 2013 Carleton College (Teaching Assistant) CHEM 123: Introductory Chemistry Fall 2009 CHEM 233: Organic Chemistry I Winter 2010, Fall 2010, Winter 2011 CHEM 234: Organic Chemistry II Spring 2010, Spring 2011 MENTORING EXPERIENCE Graduate Student Mentor, Holland Research Group 2017–2020 Fundamentals of Inclusive Teaching (Yale Center for Teaching and Learning) Fall 2018 Teaching in Science and Engineering: The College Classroom (UW–Madison Dept.
    [Show full text]
  • Photoredox Catalysis Photoredox Catalysis: a Mild, Operationally Simple Approach to the Synthesis of A-Trifluoromethyl Carbonyl Compounds Phong V
    DOI: 10.1002/anie.201101861 Photoredox Catalysis Photoredox Catalysis: A Mild, Operationally Simple Approach to the Synthesis of a-Trifluoromethyl Carbonyl Compounds Phong V. Pham, David A. Nagib, and David W. C. MacMillan* The unique physical and chemical advantages conferred by the CÀF bond have led to the broad exploitation of this motif throughout the pharmaceutical,[1] materials,[2] and agrochem- ical[3] sectors. In drug design, for instance, incorporation of polyfluorinated alkyl groups, such as CF3 moieties, can profoundly impact the activity, metabolic stability, lipophilic- ity, and bioavailability of lead compounds.[1,4] Not surpris- ingly, the development of methods for the production of carbonyl-based synthons bearing a-CF3 substitution has emerged as a central objective in the field of chemical synthesis. Although important recent advances have been made toward this goal, there are currently few operationally simple methods for the conversion of enolates (or enolate equivalents) to a-trifluoromethylated carbonyl motifs. Stan- dard alkylation methods are generally not productive, due to the negative polarization of the trifluoromethyl moiety, thus specially tailored reagents have been developed to furnish an trifluoromethylation of a range of enolates or enolate [5] electrophilic CF3 equivalent. Alternatively, in recent years, a equivalents [Eq. (1)]. In this context, we elected to employ set of radical (Et3B/O2) and organometallic (Rh-catalyzed) enolsilanes and silylketene acetals as suitable enolic sub- approaches have been
    [Show full text]
  • Enantioselective Alkylation of Aldehydes
    Angewandte Chemie International Edition: DOI: 10.1002/anie.201503789 Synthetic Methods Hot Paper German Edition: DOI: 10.1002/ange.201503789 Enantioselective a-Alkylation of Aldehydes by Photoredox Organocatalysis: Rapid Access to Pharmacophore Fragments from b- Cyanoaldehydes** Eric R. Welin, Alexander A. Warkentin, Jay C. Conrad, and David W. C. MacMillan* Abstract: The combination of photoredox catalysis and Recently, we questioned whether this dual photoredox- enamine catalysis has enabled the development of an enantio- organocatalysis platform could be translated to the asym- selective a-cyanoalkylation of aldehydes. This synergistic metric catalytic alkylation of aldehydes using a-bromo catalysis protocol allows for the coupling of two highly cyanoalkyls, a protocol that would generate b-cyanoalde- versatile yet orthogonal functionalities, allowing rapid diversi- hydes in one step. As a critical design element, we recognized fication of the oxonitrile products to a wide array of that a-bromo cyanoalkylating reagents would not be suitable medicinally relevant derivatives and heterocycles. This meth- electrophiles for most catalytic enolate addition pathways; odology has also been applied to the total synthesis of the however, the corresponding open-shell radicals, derived by lignan natural product (À)-bursehernin. one-electron reduction of a-bromonitriles, should readily undergo coupling with transiently generated chiral enamines. The enantioselective a-alkylation of carbonyl compounds In addition, the nitrile functional group offers
    [Show full text]
  • Electrochemistry and Photoredox Catalysis: a Comparative Evaluation in Organic Synthesis
    molecules Review Electrochemistry and Photoredox Catalysis: A Comparative Evaluation in Organic Synthesis Rik H. Verschueren and Wim M. De Borggraeve * Department of Chemistry, Molecular Design and Synthesis, KU Leuven, Celestijnenlaan 200F, box 2404, 3001 Leuven, Belgium; [email protected] * Correspondence: [email protected]; Tel.: +32-16-32-7693 Received: 30 March 2019; Accepted: 23 May 2019; Published: 5 June 2019 Abstract: This review provides an overview of synthetic transformations that have been performed by both electro- and photoredox catalysis. Both toolboxes are evaluated and compared in their ability to enable said transformations. Analogies and distinctions are formulated to obtain a better understanding in both research areas. This knowledge can be used to conceptualize new methodological strategies for either of both approaches starting from the other. It was attempted to extract key components that can be used as guidelines to refine, complement and innovate these two disciplines of organic synthesis. Keywords: electrosynthesis; electrocatalysis; photocatalysis; photochemistry; electron transfer; redox catalysis; radical chemistry; organic synthesis; green chemistry 1. Introduction Both electrochemistry as well as photoredox catalysis have gone through a recent renaissance, bringing forth a whole range of both improved and new transformations previously thought impossible. In their growth, inspiration was found in older established radical chemistry, as well as from cross-pollination between the two toolboxes. In scientific discussion, photoredox catalysis and electrochemistry are often mentioned alongside each other. Nonetheless, no review has attempted a comparative evaluation of both fields in organic synthesis. Both research areas use electrons as reagents to generate open-shell radical intermediates. Because of the similar modes of action, many transformations have been translated from electrochemical to photoredox methodology and vice versa.
    [Show full text]
  • A Synergistic LUMO Lowering Strategy Using Lewis Acid Catalysis in Water to Enable Photoredox Cite This: Chem
    Chemical Science View Article Online EDGE ARTICLE View Journal | View Issue A synergistic LUMO lowering strategy using Lewis acid catalysis in water to enable photoredox Cite this: Chem. Sci.,2018,9,7096 – All publication charges for this article catalytic, functionalizing C C cross-coupling of have been paid for by the Royal Society † of Chemistry styrenes Elisabeth Speckmeier, Patrick J. W. Fuchs and Kirsten Zeitler * Easily available a-carbonyl acetates serve as convenient alkyl radical source for an efficient, photocatalytic cross-coupling with a great variety of styrenes. Activation of electronically different a-acetylated acetophenone derivatives could be effected via LUMO lowering catalysis using a superior, synergistic combination of water and (water-compatible) Lewis acids. Deliberate application of fac-Ir(ppy)3 as photocatalyst to enforce an oxidative quenching cycle is crucial to the success of this (umpolung type) transformation. Mechanistic particulars of this dual catalytic coupling reaction have been studied in detail using both Stern–Volmer and cyclic voltammetry Creative Commons Attribution-NonCommercial 3.0 Unported Licence. Received 12th May 2018 experiments. As demonstrated in more than 30 examples, our water-assisted LA/photoredox Accepted 17th July 2018 catalytic activation strategy allows for excess-free, equimolar radical cross-coupling and subsequent DOI: 10.1039/c8sc02106f formal Markovnikov hydroxylation to versatile 1,4-difunctionalized products in good to excellent rsc.li/chemical-science yields. redox properties: with an oxidation potential of only 0.66 V vs. Introduction À SCE (Eox(Brc/Br ) ¼ 0.66 V) mesolytically cleaved bromide Visible light photocatalysis as a powerful tool for the selective anions can easily get oxidized to the corresponding bromine This article is licensed under a generation of radicals has given rise to numerous unprece- radicals and hence potentially may also form elemental Br2 by 8–10 dented C–C-coupling reactions in recent years.1 Especially alkyl most common photocatalysts.
    [Show full text]
  • Merging Photoredox Catalysis with Organocatalysis
    REPORTS 8. C. Resini, T. Montanari, G. Busca, J.-M. Jehng, 17. M. Salmeron, R. Schlögl, Surf. Sci. Rep. 63, 169 (2008). für Synchrotronstrahlung for support of in situ XPS I. E. Wachs, Catal. Today 99, 105 (2005). 18. T. I. T. Okpalugo, P. Papakonstantinou, H. Murphy, measurements; and M. A Smith for helpful discussions. 9. T. G. Alkhazov, E. A. Ismailov, A. Yu, A. I. Kozharov, J. McLaughlin, N. M. D. Brown, Carbon 43, 153 (2005). Supported by the CANAPE project of the 6th Framework Kinet. Katal. 19, 611 (1978). 19. L. M. Madeira, M. F. Portela, Catal. Rev. 44, 247 (2002). Programme of European Commission and the ENERCHEM 10. M. S. Kane, L. C. Kao, R. K. Mariwala, D. F. Hilscher, 20. F. Atamny et al., Mol. Phys. 76, 851 (1992). project of the Max Planck Society. H. C. Foley, Ind. Eng. Chem. Res. 35, 3319 (1996). 21. M. L. Toebes, J. M. P. van Heeswijk, J. H. Bitter, 11. M. F. R. Pereira, J. J. M. Órfão, J. L. Figueiredo, A. J. van Dillen, K. P. de Jong, Carbon 42, 307 (2004). Appl. Catal. A 218, 307 (2001). 22. A. M. Puziy, O. I. Poddubnaya, A. M. Ziatdinov, Appl. Surf. Supporting Online Material www.sciencemag.org/cgi/content/full/322/5898/73/DC1 12. J. Zhang et al., Angew. Chem. Int. Ed. 46, 7319 (2007). Sci. 252, 8036 (2006). Materials and Methods 13. G. Mestl, N. I. Maksimova, N. Keller, V. V. Roddatis, 23. S. J. Clark et al., Z. Kristallogr. 220, 567 (2005). R. Schlögl, Angew.
    [Show full text]
  • Iron-Catalyzed Amino-Oxygenation and Aminofluorination of Olefins
    Georgia State University ScholarWorks @ Georgia State University Chemistry Theses Department of Chemistry 8-11-2015 Iron-Catalyzed Amino-Oxygenation and Aminofluorination of Olefins Jeffrey Sears [email protected] Follow this and additional works at: https://scholarworks.gsu.edu/chemistry_theses Recommended Citation Sears, Jeffrey, "Iron-Catalyzed Amino-Oxygenation and Aminofluorination of Olefins." Thesis, Georgia State University, 2015. https://scholarworks.gsu.edu/chemistry_theses/77 This Thesis is brought to you for free and open access by the Department of Chemistry at ScholarWorks @ Georgia State University. It has been accepted for inclusion in Chemistry Theses by an authorized administrator of ScholarWorks @ Georgia State University. For more information, please contact [email protected]. IRON-CATALYZED AMINO-OXYGENATION AND AMINOFLUORINATION OF OLEFINS by JEFFREY D. SEARS Under the Direction of Hao Xu, PhD ABSTRACT The first chapter of the thesis describes an iron(II)-catalyzed intermolecular amino- oxygenation of alkenes. This amino-oxygenation method is found to be compatible with a broad range of synthetically valuable alkenes and affords the corresponding 1,2-amino alcohols with excellent regio- and diastereoselectivity. Additionally, practical synthetic procedures for the amino-oxygenation of styrene, a fully functionalized glycal, and indene are described. The second chapter of the thesis describes a regioselective and diastereoselective iron(II)-catalyzed intermolecular aminofluorination of alkenes using nucleophilic fluorinating reagents. This method affords new vicinal amino fluorides that were previously difficult to prepare. In both the amino-oxygenation and aminofluorination reactions, bench-stable hydroxylamine derivatives functioned as both the oxidant and amination reagents. Preliminary mechanistic studies suggested that an iron-nitrenoid is a possible reactive intermediate on both reaction pathways.
    [Show full text]
  • Visible Light Photoredox Catalysis with Transition Metal Complexes: Applications in Organic Synthesis Christopher K
    Review pubs.acs.org/CR Visible Light Photoredox Catalysis with Transition Metal Complexes: Applications in Organic Synthesis Christopher K. Prier, Danica A. Rankic, and David W. C. MacMillan* Merck Center for Catalysis at Princeton University, Princeton, New Jersey 08544, United States References 5360 1. INTRODUCTION CONTENTS A fundamental aim in the field of catalysis is the development 1. Introduction 5322 of new modes of small molecule activation. One approach 2+ toward the catalytic activation of organic molecules that has 2. Photochemistry of Ru(bpy)3 5323 3. Net Reductive Reactions 5324 received much attention recently is visible light photoredox 3.1. Reduction of Electron-Poor Olefins 5324 catalysis. In a general sense, this approach relies on the ability of 3.2. Reductive Dehalogenation 5326 metal complexes and organic dyes to engage in single-electron- 3.3. Reductive Cleavage of Sulfonium and transfer (SET) processes with organic substrates upon Sulfonyl Groups 5328 photoexcitation with visible light. 3.4. Nitrogen Functional Group Reductions 5329 Many of the most commonly employed visible light 3.5. Radical Cyclizations 5330 photocatalysts are polypyridyl complexes of ruthenium and iridium, and are typified by the complex tris(2,2′-bipyridine) 3.6. Reductive Epoxide and Aziridine Opening 5331 2+ 3.7. Reduction-Labile Protecting Groups 5331 ruthenium(II), or Ru(bpy)3 (Figure 1). These complexes 4. Net Oxidative Reactions 5332 4.1. Functional Group Oxidations 5332 4.2. Oxidative Removal of the PMB Group 5334 4.3. Oxidative Biaryl Coupling 5335 4.4. Oxidative Generation of Iminium Ions 5335 4.5. Azomethine Ylide [3 + 2] Cycloadditions 5338 4.6.
    [Show full text]
  • Read Laura's Thesis Chapter
    Communicating Research to the General Public At the March 5, 2010 UW-Madison Chemistry Department Colloquium, Prof. Bassam Z. Shakhashiri, the director of the Wisconsin Initiative for Science Literacy (WISL), encouraged all UW-Madison chemistry Ph.D. candidates to include a chapter in their Ph.D. thesis communicating their research to non-specialists. The goal is to explain the candidate’s scholarly research and its significance to a wider audience that includes family members, friends, civic groups, newspaper reporters, program officers at appropriate funding agencies, state legislators, and mem- bers of the U.S. Congress. Over 20 Ph.D. degree recipients have successfully completed their theses and included such a chapter. WISL encourages the inclusion of such chapters in all Ph.D. theses everywhere through the cooperation of Ph.D. candidates and their mentors. WISL is now offering additional awards of $250 for UW-Madison chemistry Ph.D. candidates. The dual mission of the Wisconsin Initiative for Science Literacy is to promote literacy in science, mathematics and technology among the general public and to attract future generations to careers in research, teaching and public service. UW-Madison Department of Chemistry 1101 University Avenue Madison, WI 53706-1396 Contact: Prof. Bassam Z. Shakhashiri [email protected] www.scifun.org May 2014 Controlling the Chemistry of Photogenerated Radicals with Lewis and Brønsted Acid Co-Catalysts By Laura Ruiz Espelt A dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy (Chemistry) at the UNIVERSITY OF WISCONSIN!MADISON 2014 Date of final oral examination: 08/06/2014 The dissertation is approved by the following members of the Final Oral Committee: Tehshik Yoon, Professor, Chemistry Clark Landis, Professor, Chemistry Shannon Stahl, Professor, Chemistry Jennifer Schomaker.
    [Show full text]
  • Badger Chemist the Newsletter of the Department of Chemistry at the University of Wisconsin-Madison
    Badger Chemist The Newsletter of the Department of Chemistry at the University of Wisconsin-Madison Established 1953, No. 57, 2014 BADGER CHEMIST Ten People, Ten Stories Ever since joining the faculty at the University of Wisconsin-Madison 25 years ago, one of the things that has most impressed me is the astounding variety of science, classes, and other activities that happen in our department each day. If you were to explore the Chemistry Building and talk to 10 people, each one might easily tell you a different story about an exciting new research project, a meaningful class experience, a poster or publication in progress, or a new program for students or the community. With this issue of the Badger CONTENTS Chemist, we aim to give you a taste of this great diversity of teaching, research, and outreach. New Badger Chemists .................................... 2 Whether you have fond memories of learning the ins and outs Alumni News ................................................... 4 of the department’s chemical instruments (page 15), you want to Chemistry News .............................................. 5 find out the latest update on the Chemistry Building Project (page Awards and Honors ....................................... 11 Features ......................................................... 15 6), you’re curious what chemistry majors are learning in the lab Shakhashiri ACS Presidency Reflections ...... 19 these days (page 17), or you want to meet our newest professor New Faculty Profile ......................................
    [Show full text]
  • 42 National Organic Chemistry Symposium Table of Contents
    42nd National Organic Chemistry Symposium Princeton University Princeton, New Jersey June 5 – 9, 2011 Table of Contents Welcome……………………………………………………………………………….......... 2 Sponsors / Exhibitors…..……………………………………………………………........... 3 DOC Committee Membership / Symposium Organizers………………………….......... 5 Symposium Program (Schedule)……...…………………………………………….......... 9 The Roger Adams Award…………………………………………………………….......... 14 Plenary Speakers………………………………………………………………………........ 15 Lecture Abstracts..…………………………………………………………………….......... 19 DOC Graduate Fellowships……………………………………………………………....... 47 Poster Titles…………………………...……………………………………………….......... 51 General Information..………………………………………………………………….......... 93 Attendees………………………………..……………………………………………........... 101 Notes………..………………………………………………………………………….......... 117 (Cover Photo by Chris Lillja for Princeton University Facilities. Copyright 2010 by the Trustees of Princeton University.) -------42nd National Organic Chemistry Symposium 2011 • Princeton University Welcome to Princeton University On behalf of the Executive Committee of the Division of Organic Chemistry of the American Chemical Society and the Department of Chemistry at Princeton University, we welcome you to the 42nd National Organic Chemistry Symposium. The goal of this biennial event is to present a distinguished roster of speakers that represents the current status of the field of organic chemistry, in terms of breadth and creative advances. The first symposium was held in Rochester NY, in December 1925, under the auspices of
    [Show full text]
  • Difunctionalization of Alkenes and Alkynes Via Intermolecular Radical and Nucleophilic Additions
    molecules Review Difunctionalization of Alkenes and Alkynes via Intermolecular Radical and Nucleophilic Additions Hongjun Yao 1,†, Wenfei Hu 2,† and Wei Zhang 2,* 1 College of Biological Science and Technology, Beijing Forestry University, 35 Qinghua East Road, Beijing 100083, China; [email protected] 2 Department of Chemistry, University of Massachusetts Boston, 100 Morrissey Boulevard, Boston, MA 02125, USA; [email protected] * Correspondence: [email protected]; Tel.: +1-617-287-6147 † These authors contributed equally to this work. Abstract: Popular and readily available alkenes and alkynes are good substrates for the preparation of functionalized molecules through radical and/or ionic addition reactions. Difunctionalization is a topic of current interest due to its high efficiency, substrate versatility, and operational simplicity. Presented in this article are radical addition followed by oxidation and nucleophilic addition reactions for difunctionalization of alkenes or alkynes. The difunctionalization could be accomplished through 1,2-addition (vicinal) and 1,n-addition (distal or remote) if H-atom or group-transfer is involved in the reaction process. A wide range of moieties, such as alkyl (R), perfluoroalkyl (Rf), aryl (Ar), hydroxy (OH), alkoxy (OR), acetatic (O2CR), halogenic (X), amino (NR2), azido (N3), cyano (CN), as well as sulfur- and phosphorous-containing groups can be incorporated through the difunctional- ization reactions. Radicals generated from peroxides or single electron transfer (SET) agents, under photoredox or electrochemical reactions are employed for the reactions. Keywords: difunctionalization; radical; nucleophilic; alkene; alkyne; photoredox; single electron transfer; vicinal-difunctionalization; distal-difunctionalization; photoredox; electrochemical reaction Citation: Yao, H.; Hu, W.; Zhang, W. Difunctionalization of Alkenes and Alkynes via Intermolecular Radical and Nucleophilic Additions.
    [Show full text]