IV. the Synthesis of (±)-Horsfiline
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Research Collection Doctoral Thesis Novel approach to spiro-pyrrolidine-oxindoles and its application to the synthesis of (±)-horsfiline and (-)-spirotryprostatin B Author(s): Marti, Christiane Publication Date: 2003 Permanent Link: https://doi.org/10.3929/ethz-a-004489068 Rights / License: In Copyright - Non-Commercial Use Permitted This page was generated automatically upon download from the ETH Zurich Research Collection. For more information please consult the Terms of use. ETH Library Diss. ETH No. 15001 Novel Approach to Spiro-Pyrrolidine-Oxindoles and its Application to the Synthesis of (±)-Horsfiline and (–)-Spirotryprostatin B A dissertation submitted to the SWISS FEDERAL INSTITUTE OF TECHNOLOGY ZÜRICH for the degree of Doctor of Natural Sciences Presented by Christiane MARTI Dipl. Ing. ECPM Strasbourg born 25. August 1972 in Stuttgart, Germany Accepted on the recommendation of Prof. Dr. Erick M. Carreira, examiner Prof. Dr. Hans-Jürg Borschberg, co-examiner Karin, Gerhard und Thomas in grosser Dankbarkeit gewidmet Und ist schon jemals ein Ziegel so vom Dach gefallen, wie es das Gesetz vorschreibt? Niemals! Nicht einmal im Laboratorium zeigen sich die Dinge so wie sie sollen. Sie weichen regellos nach allen Richtungen davon ab, und es ist einigermaβen eine Fiktion, daβ wir das als Fehler der Ausführung ansehen und in der Mitte einen wahren Wert vermuten. Robert Musil Acknowledgements My dissertation at ETH was a real learning experience that was enjoyable most of the time. Any successes during this time are also due to substantial support from others. I therefore express my deepest thanks to: Prof. Dr. Erick M. Carreira ― I benefited his guidance and support throughout the course of my thesis. He was always open for scientific discussions, has an endless supply of ideas, and allowed me the freedom to decide the direction of the project. At times when I was willing to give up; he somehow found a way of motivating me to reach the final goal. Prof. Dr. Hans-Jürg Borschberg ― He accepted the co-examination of my thesis and his interest in this work led to a thoroughly corrected manuscript. Alec Fettes ― He read and corrected my manuscript and thereby substantially improved this thesis not only in grammar and spelling, but also with clever suggestions on the presentation of the content. Christian Fischer ― His diploma work presents a noteworthy contribution to this thesis. His enthusiastic working attitude and his conscientious but efficient preparative work impressed me deeply. Brigitte Brandenberg, Philipp Zumbrunnen and Prof. Dr. Bernhard Jaun ― The spectra from the NMR-service had always a wonderful appearance, even when I only submitted the tiniest amounts. Without help interpreting some of the spectral data, I would have been lost. Rolf Häflinger, Oswald Greter, Oliver Scheidegger and Dr. Walter Amrein ― They measured my MS spectra and answered all associated questions. Volker Gramlich and Paul Seiler ― They both solved X-ray crystal structures relevant to this project and had the time to discuss their results with me in detail. The members of the ETH staff responsible for ‘Schalter’, ‘Glaswäscherei’, ‘Entsorgung’ are gratefully acknowledged for prompt service always accompanied with a smile and a friendly word. The students in the OCP1 synthesized multigram quantities of my starting material. The Carreira group is acknowledged for creating an overall pleasant working atmosphere. My special thanks go to: Claudia Dörfler and Franziska Peyer ― They solved every administrative problem and did all the paperwork. Also they always had an open ear for problems of the group and its individuals. Jeffrey Bode, Alec Fettes, Dieter Muri, Tobias Ritter ― They have all been more than just co-workers, lab-mates or ‘Settlers’ but real friends. Jeff is a wonderful person and a brilliant chemist. His suggestions on my project were always very helpful. Alec and I went a long way together (St Gallen-Zürich, Sola Duo, 8 h 15 min). His suggestions on my chemistry decided the success of this project. Didi and Tobi are real sportsman and I enjoyed playing volley and squash with them or having them chase me though the forest (jogging), up the mountains (hiking in summer) und down the hills (skiing in winter). Roger Fässler, Patrick Aschwanden, Jürg Oetiker and Stephan Schnidrig ― They where always in a good mood and made the atmosphere in the lab an enjoyable one. Aschi is the best PC-expert and was always solving my problems with ‘this stupid computer’. My friends outside of the Carreira group also contributed significantly to this thesis by encouraging me whenever it was necessary. My special thanks go to Anja Schürch, Sibylle Steimen and Ulee Speicher, but also to my friends back in Germany and France and from Volley KSOe. Many thanks go also to my family for their support and love. Last but not least: Thomas, I thank you very much for you support and love and for standing at my side all the time. Without you, I would not have made it. Publications and Presentations Alec Fettes, Christiane Marti and Erick M. Carreira “Catalytic Asymmetric Aldol Reactions” Org. Reactions, manuscript in preparation. Christiane Marti and Erick M. Carreira “Total Synthesis of (–)-Spirotryprostatin B, Synthesis and Related Studies” manuscript in preparation. Christiane Marti and Erick M. Carreira “Construction of Spiro[Pyrrolidine-3,3’-Oxindoles] ― Recent Applications to the Synthesis of Oxindole Alkaloids” Eur. J. Org. Chem. manuscript submitted. Christiane Meyers and Erick M. Carreira “Total Synthesis of (–)-Spirotryprostatin B” Angew. Chem. Int. Ed. in press. Christian Fischer, Christiane Meyers and Erick M. Carreira “Efficient Synthesis of (±)-Horsfiline through the MgI2-Catalysed Ring-Expansion Reaction of a Spiro[cyclopropane-1,3’-indol]-2’-one” Helv. Chim. Acta 2000, 83, 1175. Phil B. Alper, Christiane Meyers, Andreas Lerchner, Dionicio R. Siegel and Erick M. Carreira ”Facile, Novel Methodology for the Synthesis of Spiro[pyrrolidin-3,3’-oxindoles]: Catalyzed Ring-Expansion Reactions of Cyclopropanes by Aldimines” Angew. Chem. Int. Ed. 1999, 38, 3186. Christiane Meyers, Phil B. Alper, Christian Fischer and Erick M. Carreira “Novel Methodology for the Synthesis of Spiro-Oxindoles” Poster presentation; Bayer Informationstage, Bayer AG (Germany), July 2000. Christiane Meyers, Phil B. Alper and Erick M. Carreira “Novel Methodology for the Synthesis of Pyrrolidine-spiro-Oxindole Ring Systems” Poster presentation; Drug Discovery, Pfizer (UK), September 1999 Abstract The spiro-pyrrolidine-oxindole ring system is a recurring structural element that has been identified in a number of cytostatic alkaloids. These spiro-fused ring systems embody stereochemical and structural complexities that continue to challenge the synthetic chemist. In this thesis the development of a novel approach to spiro-pyrrolidine-oxindoles by MgI2-catalyzed ring-expansion reaction of spiro-cyclopropyl-oxindole I and a number of N-alkyl- as well as N-aryl-sulfonyl aldimines II is presented (Scheme A). MgI2 acts as a bifunctional catalyst: R' MgI2 (10-20 mol%), N THF nucleophilic R I N O R' N O activation Bn N Bn I III Mg activation by R N O I Lewis acid II major diastereomer Bn ca. 80:20 Scheme A: Ring expansion of spiro-cyclopropyl-oxindole I with aldimines II catalyzed by MgI2. MgI2 acts as a bifunctional catalyst wherein the Lewis-acidic metal and the nucleophilic counterion operate in synergy. The resulting spiro-pyrrolidine-oxindole ring systems III were obtained in good yields and with high diastereoselectivities. MeO MeO NMe MeO NMe MgI2 (5.5 mol%), THF 83 % 41 % N O N O overall N O Bn Me Bn H N IV horsfiline MeN NMe V Scheme B: Synthesis of (±)-horsfiline. Our interest in the class of spiro-pyrrolidine-oxindole natural products as well as the scope of the ring-expansion reaction led us to apply this method in the synthesis of horsfiline and spirotryprostatin B. The synthetic route to (±)-horsfiline demonstrates the use of 1,3,5-trimethyl-1,3,5-triazine (V) as an equivalent for N-methylmethanimine under the conditions of the ring-expansion reaction. The synthesis afforded (±)-horsfiline in 41% yield over 5 steps via N-benzyl-spiro-cyclopropyl-oxindole (IV) (Scheme B). In order to access the spirotryprostatin B core in a straightforward fashion, we could establish that C9-substituted (spirotryprostatin numbering) spiro-pyrrolidine-oxindole derivative VIII can be obtained in good yield from substituted cyclopropane VI and imine VII. The diastereomer distribution favors VIII possessing the required C3–C18 anti- relationship (6:1). The corresponding syn-diastereomers were found to be converted to VIII by refluxing in acetic acid. Resolution is achieved by peptide coupling with N-Boc- L-proline chloride to furnish IX. MeHC MeHC MeHC O 9 O BocN N MgI2, THF HN 18 N HN N + 3 H N O O H TIPS VI VII TIPS TIPS VIII IX AcOH, ∆ + isomers O CO2Me CO2Me O N O BocN Julia-Kociensky O BocN olefination HN 3 N HN N HN N H 18 H H O O O Me Me O Me Me spirotryprostatin B XI X Scheme C: Total synthesis of (–)-spirotryprostatin B. Introduction of the prenyl side chain was accomplished by olefination of aldehyde XII by Julia–Kocieńsky reaction to give XI, although similar transformations proved difficult in earlier syntheses. Intermediate XI was then converted to spirotryprostatin B (Scheme C). The synthetic sequence was performed in 16 steps (3.4% overall yield) and is a powerful demonstration of the utility of the ring-expansion method. Zusammenfassung Das Spiro-Pyrrolidin-Oxindol Ringsystem ist ein Strukturelement, welches in einigen zytostatisch wirkenden Alkaloiden identifiziert wurde. Die stereochemische und strukturelle Komplexität dieser Systeme machen Spiro-Pyrrolidin-Oxindole zu attraktiven Zielmolekülen für den organischen Synthetiker. Diese Abhandlung beschreibt die Entwicklung einer neuartigen Methode, die über eine MgI2-katalysierte Ring- Erweiterungs-Reaktion von Spiro-Cyclopropyl-Oxindol I mit verschiedenen N-Alkyl- bzw N-Aryl-Sulfonyl-Aldiminen II zu Spiro-Pyrrolidin-Oxindolen führt (Schema A).