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Enantioselective Epoxidation Reactions Using Chiral Ammonium Salts

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Enantioselective Epoxidation Reactions Using Chiral Ammonium Salts JOHANNES KEPLER UNIVERSITÄT LINZ JKU Faculty of Engineering and Natural Sciences Enantioselective epoxidation reactions using chiral ammonium salts Master‘s Thesis to confer the academic degree of Diplom-Ingenieurin in the Master‘s program Technical Chemistry Submitted by: Katharina Zielke At the: Institute of Organic Chemistry Advisor: Assoc. Univ.-Prof. Dr. Mario Waser Linz, October 2015 1 Contents Eidesstattliche Erklärung 5 Acknowledgements 6 Curriculum Vitae 7 Abstract 9 Zusammenfassung 10 1 Introduction 11 1.1 Epoxides ..................................... 11 1.2 Epoxides from alkenes ............................. 11 1.2.1 Prilezhaev epoxidation ......................... 12 1.2.2 Sharpless epoxidation ......................... 13 1.2.3 Jacobsen-Katsuki epoxidation ..................... 15 1.2.4 Shi asymmetric epoxidation ....................... 17 1.3 Epoxides from carbonyl compounds ...................... 18 1.3.1 The Darzens glycidic ester condensation ............... 19 1.3.2 The Corey-Chaykovsky reaction .................... 20 1.3.2.1 Diastereoselectivity in Sulfur-ylide-mediated reactions . 21 1.3.2.2 Enantioselectivity in sulfur-ylide-mediated reactions ..... 23 1.3.2.3 Catalytic use of sulfur ylides ................. 24 1.4 Ammonium ylides in epoxidation reactions ................... 27 1.4.1 Investigations by Jonczyk et al. and Kimachi et al. .......... 27 1.4.2 Diastereoselectivity in reactions of ammonium ylides with aldehydes 29 2 Results and Discussion 30 2.1 Motivation of this work .............................. 30 2.2 Previous experiments from our group members ................ 30 2.3 DABCO-derived chiral ammonium acetamides ................ 33 2.3.1 Reactions using the DABCO-derivative 62 ............... 33 2.3.2 Reactions using the camphor-derivative 68 .............. 34 2 2.4 Proline-derived chiral ammonium acetamides ................. 35 2.4.1 Synthesis of different proline-based ammonium salts and their use . 36 2.4.2 Variations on R1 ............................. 37 2.4.3 Variations on R2 ............................. 39 2.4.4 Attempted synthesis of further ammonium salts ............ 40 2.4.5 Screening of the best-suited reaction conditions ............ 42 2.4.6 Crystal structure of the synthesized ammonium salt 63g ....... 43 2.4.7 Application scope ............................ 44 2.4.8 Attempted catalytic use of the amine .................. 47 2.4.9 Recycling of the amine after epoxidation reactions .......... 47 2.5 Summary and Outlook ............................. 49 3 Experimental part 51 3.1 General remarks ................................. 51 3.2 Syntheses .................................... 51 3.2.1 Synthesis of ((2S,3S)-2,3-diphenyl-1,4-diazabicyclo[2.2.2]octane) 65 51 3.2.2 Attempted synthesis of camphor-based amine 68 ........... 53 3.2.3 Synthesis of (2-bromo-N,N-diethylacetamide) ............. 55 3.2.4 Protection of L-proline .......................... 55 3.2.5 General procedure I: Grignard-reaction ................ 57 3.2.6 General procedure II: Deprotection of the arylated amines ...... 57 3.2.7 General procedure III: Closing the second 5-membered ring ..... 58 3.2.8 General procedure IV: Synthesis of chiral ammonium acetamides . 58 3.2.9 Synthesis of DABCO-derived ammonium salt 62 ........... 59 3.2.10 Synthesis of ammonium salt 63a (R1 = phenyl, R2 = H) ........ 60 3.2.11 Synthesis of ammonium salt 63b (R1 = naphthyl, R2 = H) ....... 63 3.2.12 Synthesis of ammonium salt 63c (R1 = biphenyl, R2 = H) ....... 66 3.2.13 Synthesis of ammonium salt 63d (R1 = p-OMe-phenyl, R2 = H) . 70 3.2.14 Synthesis of ammonium salt 63e (R1 = p-F-phenyl, R2 = H) ..... 73 1 2 3.2.15 Synthesis of ammonium salt 63f (R = p-CF3-phenyl, R = H) .... 76 3.2.16 Synthesis of ammonium salt 63g (R1 = phenyl, R2 = cyclohexyl) . 80 3.2.17 Synthesis of ammonium salt 63h (R1 = phenyl, R2 = tert-butyl) .... 82 3.2.18 Synthesis of ammonium salt 63i (R1 = phenyl, R2 = n-butyl) ..... 84 3 3.2.19 Synthesis of ammonium salt 63j (R1 = phenyl, R2 = benzyl) ..... 85 3.2.20 General procedure V .......................... 88 3.2.21 Epoxidation reactions .......................... 88 3.2.21.1 Epoxidation reaction for testing all synthesized ammonium salts 88 3.2.21.2 Application scope of the asymmetric epoxidation ...... 89 4 Literature 95 4 Eidesstattliche Erklärung Ich erkläre an Eides statt, dass ich die vorliegende Diplomarbeit selbstständig und ohne fremde Hilfe verfasst, andere als die angegebenen Quellen und Hilfsmittel nicht benutzt bzw. die wörtlich sinngemäß entnommenen Stellen als solche kenntlich gemacht habe. Die vorliegende Diplomarbeit ist mit dem elektronisch übermittelten Textdokument identisch. Linz, Oktober 2015 5 Acknowledgements First, I would like to thank my parents for giving me the opportunity to study and my whole family for their love and support. I am very thankful to be blessed with very good friends who sometimes forced me to take some time off from studies when I needed to. I am very thankful to Univ. Prof. Dr. Norbert Müller for giving me the opportunity to work at his institute. Furthermore, I would like to thank all colleagues from the Institute of Organic Chemistry for the relaxed and friendly working atmosphere. Special gratitude goes to Assoc. Prof. Dr. Waser for his whole support, encouragement and advice. Last but not least, I would like to thank my study colleagues for their support and friendship not only during this thesis but through my whole studies. 6 Curriculum Vitae Personal Data Date of Birth November 13, 1990 Place of Birth Wels Nationality Austria School education 09/1997 - 07/2001 VS Stadl-Paura 09/2001 - 07/2005 Hauptschule Stadl-Paura 09/2005 - 07/2010 HAK Lambach June, 2010 Higher education entrance qualification University education 10/2010 - 02/2014 Bachelor’s programme “Technische Chemie” at the JKU Linz 02/2014 - now Master’s programme “Technische Chemie” Work experience abroad 07/2014 - 09/2014 Hokkaido University, Japan; Practical course ”Praktikum aus Chemis- cher Technologie Anorganischer Stoffe” 7 Work experience 07/2010 - 09/201 Sport Eybl & Sports Experts GmbH, office work 10/2010 - 04/2011 Sport Eybl & Sports Experts GmbH, part-time office work 08/2011 - 09/2011 EWE Küchen, production 07/2012 - 09/2012 BWT Austria GmbH, laboratory work, testing of ion-exchange- chomatography 11/2012 - 01/2013 Tutorium “Praktikum aus Allgemeiner Chemie” 05/2013 - 06/2013 Tutorium “Praktikum Chemie für Kunststofftechnik” 07/2013 - 09/2013 Sandoz, Oncology Incectables, laboratory work, quality control of in- coming chemicals 09/2013 - 10/2015 Forstner, part-time job as waitress 11/2013 - 02/2014 Tutorium “Praktikum aus Allgemeiner Chemie” 05/2014 - 06/2014 Tutorium “Praktikum Chemie für Kunststofftechnik” 11/2014 - 01/2015 Tutorium “Praktikum aus Allgemeiner Chemie” 05/2015 - 06/2015 Tutorium “Praktikum Chemie für Kunststofftechnik” 05/2015 - 06/2015 Tutorium “Praktikum aus Organischer Chemie II” 04/2015 - 05/2015 Tutorium “Praktikum aus Organischer Chemie für Molekulare Biolo- gen” 10/2015 - 01/2016 Tutorium “Praktikum aus Organischer Chemie I” 8 Abstract During this master thesis the enantioselective synthesis of epoxides was investigated. Epox- ides are very important structures not only for synthetic strategies, but they are also found in many natural products. Because these three-membered rings are so important, several different approaches for their synthesis have been developed. Epoxides are usually syn- thesized starting either from alkenes or aldehydes. Known reactions starting from alkenes are the Prilezhaev, the Sharples, the Jacobsen-Katsuki and the Shi-epoxidation. Famous examples, which start from aldehydes, are the Darzens reaction and the Corey-Chaykovsky reaction. Over the last years, the synthesis of epoxides using ammonium ylides - which are generated from ammonium salts - was reported. The mechanism is closely related to the Corey-Chaykovsky-reaction because the reacting species in both cases are ylides. Diastereoselective approaches for the synthesis of glycidic amides using ammonium ylides have been developed. It was shown that amide-stabilized ylides are very good educts and an enantioselective synthesis of epoxides using chiral ammonium ylides was developed. Promising results were obtained using a DABCO-derivative and an L-Proline-derivative. In the case of the DABCO-derivative very high enantioselectivities but low yields and for the L-Proline derivative moderate enantioselectivities but high yields were achieved. The next step was to improve these results which was first attempted with the DABCO- derivative. However, no better results were obtained. The reaction conditions were opti- mized for the best known L-proline ammonium salt. After finding the best-suited reaction conditions, different ammonium salts for the L-proline derivative were synthesized, the best one showing high enantioselectivities (86 %) in combination with a high yield (88 %) in the tested epoxidation reaction. The reaction conditions were again optimized resulting in even higher enantioselectivity, but at lower yields. The application scope of this promising am- monium salt was tested. High yields and enantioselectivities were obtained for most tested aldehydes, however aliphatic aldehydes performed worse than aromatic ones. 9 Zusammenfassung Ziel dieser Masterarbeit war die enantioselektive Synthese von Epoxiden. Diese cycli- schen Ether sind bekannte Strukturen welche nicht nur in vielen Naturprodukten vorkom- men, sondern auch sehr wichtige Elemente für Synthesen darstellen. Aufgrund der
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