The Double SN2' Substitution Performed on Diynes: a New
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Master thesis in organic Chemistry and catalysis The double SN2’ substitution performed on diynes: A New Reaction for the Arsenal of the Organic Chemist C.C.A. van Heerewaarden July 2017 Faculty of mathematics and natural science Stratingh Institute for Chemistry University of Groningen C.C.A. van Heerewaarden Master research thesis Date final report: 13 July 2017 Faculty of mathematics and natural science Stratingh Institute for Chemistry University of Groningen 1st assessor: Prof. Dr. Ir. A.J. Minnaard 2nd assessor: Dr. M.D. Witte Table of contents LIST OF ABBREVIATIONS & SYMBOLS ...................................................................................................... 4 SUMMARY ............................................................................................................................................... 5 1. INTRODUCTION ................................................................................................................................... 6 1.1 Carbon-carbon coupling reactions ................................................................................................ 6 1.2 Cross-coupling reactions ............................................................................................................... 6 1.3 Synthesis, characteristics and applications of dendralenes .......................................................... 9 1.4 Developments towards new reactions for dendralenes ............................................................. 12 1.5 Project aim .................................................................................................................................. 13 1.6 References ................................................................................................................................... 13 2. RESULTS & DISCUSSIONS ................................................................................................................... 16 2.1 Introduction to the double SN2’ substitution reaction on diynes ............................................... 16 2.2 Methodology & optimization ...................................................................................................... 17 2.3 Investigation of the scope of the reaction .................................................................................. 20 2.4 Proposed mechanism .................................................................................................................. 26 2.5 Dicobaltoctacarbonyl complexation............................................................................................ 29 2.6 Outlook & recommendations ...................................................................................................... 31 2.7 References ................................................................................................................................... 32 3. CONCLUSIONS ................................................................................................................................... 34 4. EXPERIMENTALS ................................................................................................................................ 35 4.1 General methods ......................................................................................................................... 35 4.2 General procedure for performing a quantitative NMR experiment .......................................... 35 4.3 Synthesis of compounds .............................................................................................................. 36 4.4 DOT study for the quantitative NMR .......................................................................................... 42 4.5 NMR spectra of isolated compounds .......................................................................................... 43 4.6 FT-IR spectra of cobalt complexes ............................................................................................... 62 4.7 GC-MS spectra of isolated ........................................................................................................... 63 4.8 X-ray parameters and spectra ..................................................................................................... 71 4.9 References ................................................................................................................................... 73 ACKNOWLEDGMENTS ........................................................................................................................... 74 LIST OF ABBREVIATIONS & SYMBOLS α - Alpha β - Beta δ - Delta 1H - Proton 13C - Carbon-13 acac - Acetylacetone Ar - Aryl BuLi - Butyllithium Cat - Catalyst Co - Cobalt CDCl3 - Chloroform-d DCM - Dichloromethane DMS - Dimethylsulfide DMSO - Dimethylsulfoxide dppe - 1,2-bis(difenylfosfino)ethane dppf - 1,1′-Ferrocenediyl-bis(diphenylphosphine) dppp - 1,3-Bis(diphenylphosphino)propane DTDA - Diene‐transmissive Diels‐Alder Et2O - Diethyl ether FT-IR - Fourier transform infrared spectroscopy GC-MS - Gas chromatography mass spectroscopy HCl - Hydrogen chloride IPr - (1,3-bis(2,6-bis(diphenylmethyl)-4-methylphenyl)imidazo-2-ylidene) J - Coupling constant MgSO4 - Magnesium sulfate NaHCO3 - Sodium bicarbonate NaSO4 - Sodium sulfate NCS - N-chlorosuccinimide Ni - Nickel NMR - Nuclear magnetic resonance Nu - Nucleophile OLED - Organic light-emitting diode OPV - Organic photovoltaic Pd - Palladium Q-NMR - Quantitative nuclear magnetic resonance r.t. - Room temperature t-BuOK - Potassium tert-butoxide t-BuOH - Tert-butyl alcohol THF - Tetrahydrofuran LIST OF ABBREVIATIONS & SYMBOLS Page 4 SUMMARY This thesis describes the newly discovered double SN2’ substitution reaction on diynes. This reaction was discovered in the search for new routes towards dendralenes utilizing double SN2’ cross-coupling reactions. In this new discovered double SN2’ substitution reaction, two Grignard nucleophiles are coupled with a diyne containing two leaving group functionalities. This coupling is performed in the presence of a Nickel catalyst and results in a rearrangement which yields a conjugated system with one internal alkyne functionality as shown below. The double SN2’ substitution reaction performed on a diyne using phenylmagnesiumbromide. In the first stage of this thesis the reaction was optimized in term of its yield in which the influence of different catalysts, ligands and their concentration was investigated. The use of nickel catalysts with a dppp ligand gave the highest yield. Next, reaction conditions like solvent, initial starting temperature, and the amount of Grignard reagent were studied. This resulted in the conclusion that THF was the best solvent, -15 oC was the best initial reaction temperature and three equivalents of Grignard reagent resulted in the highest yield. After the optimization, there was investigated which types of Grignard reagents could be used in this reaction. The use of Aromatic Grignard reagents gave moderate to good yields. Aliphatic and alkyne Grignard reagents gave little to no yield. There was also looked at the effect of different methyl substituents on the carbons in the diyne and the use of methoxy leaving groups. However, the use of chlorine leaving groups and the use of no methyl substituents gave the best yield in most cases. The purification of the products seemed problematic due to limited stability of the products at room temperature. In an effort to solve this there was attempted to stabilize the resulting products by reacting them with dicobalt octacarbonyl directly after the reaction. This strategy did not seem to stabilize the final products, but it was possible to recrystallize the resulting complex and record an x- ray diffraction spectrum which confirmed the structure. The stability of these molecules remained a problem which could only be solved by working around by storing the products at -20 oC or by introducing methyl substituents. Yields could in most cases only be reported using quantitative 1H- NMR unless the yield was high enough to isolate product. SUMMARY Page 5 1. INTRODUCTION 1.1 Carbon-carbon coupling reactions During the past decades, organic chemists have seen a wide expansion in molecules and reactions which are available to them. Many new reactions have been developed which allow the preparation of complex organic molecules with excellent regio-, chemo-, diastereo-, and enantioselectivity.[1] Especially the formation of carbon-carbon bonds has received wide attention and is considered to be the heart of organic synthesis.[2] Many different reactions have been developed during the past decades to achieve efficient carbon-carbon bond formation. Some famous examples include the Grignard reaction, the Claisen condensation, the Wittig reaction, the Michael addition and the Diels- alder reaction. Although almost any organic molecule can be made nowadays, limits are often encountered in yield and efficiency within synthetic pathways. This gave rise to questions have been raised about negative impacts on environment and society of organic chemistry and led chemists to look into further into improving selectivity, yield and methodology of reactions during the last decades. The previously mentioned carbon-carbon bond forming Grignard reaction which was first reported in 1900 is now widely applied in industry and researched throughout many group within academia.[3,4] Grignard reagents are organometallic reagents and onwards from the discovery of Grignard reagents many other organometallics