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Downloaded for Personal Non-Commercial Research Or Study, Without Prior Permission Or Charge Guthrie, Emma Jayne (2001) Novel routes to benzofurans using titanium- alkylidene chemistry. PhD thesis. http://theses.gla.ac.uk/3476/ Copyright and moral rights for this thesis are retained by the author A copy can be downloaded for personal non-commercial research or study, without prior permission or charge This thesis cannot be reproduced or quoted extensively from without first obtaining permission in writing from the Author The content must not be changed in any way or sold commercially in any format or medium without the formal permission of the Author When referring to this work, full bibliographic details including the author, title, awarding institution and date of the thesis must be given Glasgow Theses Service http://theses.gla.ac.uk/ [email protected] Novel Routes to Benzofurans using Titanium-Alkylidene Chemistry A Thesis submitted in part fulfilment of the requirements of the degree of Doctor of Philosophy Emma Jayne Guthrie Department of Chemistry University of Glasgow Glasgow G12 8QQ July 2001 tt © 2001 Emma Guthrie Dedicated to my family Acknowledgements I am grateful to the EPSRC and Aventis cropsciencefor financial support in this work. Technical support was gratefully received from Mrs Kim Wilson (microanalysis), Mr Tony Ritchie (massspectroscopy) and Mr Jim Gall and Dr David Rycroft (NMR). Also thanks to Mrs Isabel Freer for keeping the Henderson Lab organised. Thanks also to Mr Gordon McKiernan for his purification of compound 181. Particular thanks to Dr Richard Hartley for being an inspiring supervisor, and providing continuous enthusiasm through my PhD. Thanks also to Dr Mary O'Mahoney and particularly to Dr Jackie Macritchie for supervisory support from Aventis. Thank you to all of the Hartley and Robins group members I've had the pleasure to work with, especially Graeme, Stuart, Calum(n), Andy, Gordon, Neil, Christine, Fiona, Kieron, Tong, Cameron, Vikki, Siobhan and Russell who all made working in the Henderson lab so enjoyable. Also thanks to everyone who gave me support during my stay in Saffron Walden, particularly to Jackie, Ged and Mary and of course to `the Ian person' for the lifts to work! I would like acknowledge everyone I had the pleasure of working and socialising with in the Alchemists Society. And finally the `non chemists'.... to MR, Susan,Frances, Keira, Paul, John, and Emma R- thank you for the evenings of red wine and singing! Summary We have investigated two routes to functionalised benzofuransusing titanium alkylidene chemistry. The first route looked at the alkylidenation of estersi to give ß-alkoxyvinylstannanesii. A cross-coupling reaction would have given enol ether products iii, followed by an acid- induced cyclisation to give the desired benzofuransiv. R3 SnBu3 O TiCI4,TMEDA, Zn/PbCI2 -------- -- ---- 1/\ 2 R OR Bu3SnCR3I2,THE R1 OR2 i ii OPG R4 ' Pd° 4, OPG j H+ Ra -------------- R4 OR2 R R3 R3 iv iii This approach was not successful, but during the course of investigating the route, we formed the novel dimetallic reagentv, the properties of which we examined. Bu3Sn--ý MgCI v iv We looked at a second route that involved the use of thioacetals vi. Alkylidenation of followed by formed, esters "i were carried out in one case cyclisation of the enol ethers vii giving benzofuran viii (R1= Ph). O OPG PhS SPh R1AOR2 H H OPG Cp2Ti[P(OEt)3]2, THE R20 R1 vi vii 1) 6M HCI/Et2O (MeO)3CH, MeOH 2) PhMe, PPA O1 R VIII We also successfully carried out the second route on solid phase, where Wang and Merrifield resin-bound esters ix were alkylidenated. This was the first reported incidence of Takeda-style alkylidenations on solid phase. Cleavage of the resin-bound enol ethers was achieved using mild acidic conditions. This gave ketone products x. In one case ketone x was converted into benzofuran viii (R' = CH2CH2Ph) by deprotection followed by acid treatment. O OTBDMS PhS SPh O R1 R2 ix R2 ,H QOR1 OTBDMS Cp2Ti[P(OEt)3]2,THE vi ix TFA-H20(1: 1), CH2CI2 or 1% TFA in CH2CI2 30 mins OTBDMS bO R1 O i) n-Bu4NF, THF, 3h U' R1 R2 '/ Jý- ii) 1% TFA in CH2CI2 viii 30 mins X V Finally, we carried out an alternative direct cleavage to a range of benzofurans viii, by deprotecting the resin-bound enol ether ix and then cleaving with mild acid as before. OTBDMS H 1) 1M TBAF, THF, 3h \O 1 Rl j--J---O -O R' 2) 1% TFA in CH2CI2 ix or TFA: H20 (1: 1), CH2CI2 VIII 30 mins vi Contents III ACKNOWLEDGEMENTS .......................................................................................................................... SUMMARY IV ................................................................................................................................................... XI ABBREVIATIONS ....................................................................................................................................... 1 CHAPTER 1 INTRODUCTION .................................................................................................................... 1 1 1 BACKGROUND . .......................... ................................................................ ....................................... 1 2 BENZOFURANS ..................................... .................................................................. ................................ 4 1.2.1 Activity . ............................................................................................................................................ 4 1.2.1.1Pharmacological .................................................................................................................................... 6 1.2.1.2Antibacterial .......................................................................................................................................... 6 1.2.1.3 Pesticides ............................................................................................................................................... 1.2.1.4 Other Activity 7 ........................................................................................................................................ 1.2.2 Synthesis 8 .......................................................................................................................................... 8 1.2.2.1 Solution phase syntheses ............................................................................. .......................................... 8 1.2.2.2 Solid PhaseSynthesis .......................................................................................................................... 1.3 ALKYLIDENATION REACTIONS 16 .......................................................................... ..................................... 1.3.1 The Wittig 16 and related reactions ................................................................................................... 1.3.2 Titanium-based 18 reagents.......................................................................... ..................................... 1.3.3 The Petasis 21 alkylidenation ............................................................................................................. 1.3.4 The Takai 23 alkylidenation and related reactions ............................................................................ 1.3.4.1Introduction 23 ......................................................................................................................................... 1.3.4.2Mechanism 25 .......................................................................................................................................... 31 1.3.4.3Related reactions Chromium chemistry - .............................................................................................. 32 1.3.5 The Takedaalkylidenation........................................................................ .....................................36 1.4 TIN CHEMISTRY ........................................................................................ ..................................... 1.4.1 Background 36 .................................................................................................................................... 37 1.4.2 Syntheses of trialkyl(dihalomethvl)tins ..................................................... ..................................... 39 1.5 SOLID SUPPORT CHEMISTRY ............................................................................. ...................................... 1.5.1 Background 39 .................................................................................................................................... 1.5.2 Linkers/Cleavage 40 methods........................................................................ ..................................... 1.5.2.1Introduction 40 ......................................................................................................................................... 1.5.2.2Acid-Labile linkers 41 .............................................................................................................................. 1.5.2.3Photolabile linkers 42 ............................................................................................................................... 1.5.2.4Safety-Catch Linkers 43 ........................................................................................................................... 1.5.2.5Traceless linkers 44 .................................................................................................................................. 1.5.2.6Cyclative 45 cleavage.....................................................................................
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