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Approaches to Bridged Annulenes Using Both Classical and Reactive Intermediates. the Synthesis of the First Diatropic Bridged Th

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Approaches to Bridged Annulenes Using Both Classical and Reactive Intermediates. the Synthesis of the First Diatropic Bridged Th APPROACHES TO BRIDGED ANNULENES USING BOTH CLASSICAL AND REACTIVE INTERMEDIATES. THE SYNTHESIS OF THE FIRST DIATROPIC BRIDGED THIAANNULENE AND SEVERAL FUSED DIHYDROPYRENES by VIVEKANANTAN S. HER B.Sc., Madurai Kamaraj University, IN D IA 1984 M.Sc., Indian Institute of Technology, Bombay, INDIA 1986 A Dissertation Submitted in Partial Fulfilment of the Requirements for the Degree of DOCTOR OF PHILOSOPHY ill the Department of Chemistry We accept this dissertation as conforming to the required standard Dr. R. H. M itchell Dr. A. Fischer Dr. T. M. Fyles Dr. E. E. Ishiguro Dr. R. V. W illiams © VIVEKANANTAN S. IYER, 1994 University of Victoria All rights reserved. This dissertation may not he reproduced in whole or in part, by mimeograph or by any other means without the permission of the author. 11 Supervisor: Professor Dr. R. H. Mitchell ABSTRACT The successful synthesis of the first bri~ged thia[13]annulene, trans-9b,9c­ dimethyl-9b,9c-dihydrophenyleno[l,9-bc)thiophene, 120, was achieved in 11 steps, starting from 3-methylthiophene, 111. Using the external and internal proton chemical shifts of 120, it was shown unambiguously to be the first diatropic bridged thia annulene. From the proton chemical shifts of 120, its diatropicity was estimated to be about 35-40% that of dimethyldihydropyrene 12. Synthesis of the potential intermediate 2,4-bis(bromomethyl)-3-methylthiophene, 110, is expected to lead to synthese;, of a variety of new bridged annulenes. Synthesis of the quasi-biphenyiene, 155, was attempted. The precursor to 155, 1,3-bis(methoxymethyl}-2-methylbiphenylene, 170, was synthesised from 1,2- dibromobenzene, 82, in 4 steps. Attempts to convert 170 into the corresponding dibromide were unsuccessful. The synthesis of trans-14b,14c-dimethyl-14b,14c-dihydro­ benzo[l",2":3,4]cycloLata[l,2-b]naphtho[2,1,8-fgh:,mthracene, 192, was achieved from the oxa[l 7]annulene 63. A detailed nmr analysis of 192. was made using lD and 2D nmr techniques together with a bond order-chemical shift correlation for 192. From the 1Hnmr data of 1S2, using Mitchell's method, the diatropicity of biphenylene was estimated to be 50-55% that of benzene. The adduct 209, from cycloheptatriene and oxa[l 7)annulene 63, was obtained in in 60% yield, but attempted dehydration/deoxygenation reactions were unsuccessful. The cyclopropene adduct 224, was obtained in 41% yield from the oxa[l 7iannulene 63. Attempted synthesis of the benzocyclopropene fused dihydropyrene 218 gave partial success. The proton nmr data obtained frora the reaction mixture seem to indicate the lack of Mills-Nixon effect in benzocyclopropene, 181. Some attempted reactions of the dihydropyryne 62, did not yield any of the expected products. A new synthesis of symmetrical 1,2-diketones from Grignard reagents was developed. 1,2-Bis(2'-methyl-3'-methoxymethylphenyl)ethanedione, 241, was synthesised using this method. anti-9,25-Dimethylquinoxalino[l0,ll-b]-2- thia[2.3]metacyclophane-l0-ene, 287, was synthesi·md from the c'iketone 241. An X- Ill ray crystal dete1mination showed its anti geometry. The unstable trnns-14c,14d­ dimethyl-14c,14d-dihydrotribenzo[abc]phenazine, 279, was synthesised from the thiacyclophane 287. The proton nmr spectrum of 279, revealed its similarity to the naphtho[e]dihydropyrene 58. From the proton chemical shifts of 279, the diatropicity of quinoxaline was estimated to be the same as that of naphthalene. The teraryl 281 and the thiophene dioxide 296 were symhesis12d Exploratory moJel reactions of 296, resulted in various teraryls. Complexation of the thiophene dioxide 296 resulted in the complex 297. An X-ray crystal determination of 297 showed it have a syn geometry. Barrier to rotation in the teraryls obtained in this work was studied by variable temperature nmr. The results are rationalised in terms of varying ring size of arenes. Examiners: Dr. R. H. Mitchell, Supervisor (Department of Chemistry) DZ. Fi~cher, Department member (Department of Chemistry) Dr. T. M. Fyles, Department member (Department of Chemistry) Dr. E. E. Ishiguro, Out3ide member (Department of Biochemistry and Microbiology) ;;;/ Dr. R. V. Williams, External Examiner (University of Idaho) iv TABLE OF CONTENTS Abstract ii Table o f contents iv List of Tables ix L is t o f Figures x List of abbreviations xii Acknowledgements xiv Dedication xv CHAPTER ONE INTRODUCTION 1.1 Prologue 1 1.2 Detection of aromaticity 5 1.2.1 Ring current theory and aromaticity 9 1.2.2 Resonance and aromaticity 16 1.3 Estimation of aromaticity 18 1.3.1 Mitchell’s method of estimation of aromaticity 21 1.3.1.1 Benzannelation studies on DMDHP 23 1.4 Synthetic routes to DMDHP and its derivatives 33 1.4.1 The dithiacyclophane route 33 1.4.2 The dihydropyrene/oxa[ 171 annulene route 35 1.4.3 Syntheses of [elfused DMDHPs 37 V CHAPTER TWO SYNTHESES USING THE DITHIACYCLOPHANE STRATEGY 2.1 In tro d u ctio n 39 2.2 Bromomethylation of arenes 40 2.3 Search for a 1,2,3-substituted synthon 43 2.4 Synthesis of 2,4-bis(bromomethyl)-3-methylthiophene, 110 46 2.5 Synthesis of the first diatropic bridged thiaannulene 50 2.5.1 Synthesis of the dithiacyclophanes, 123 53 2.5.2 an£i-9,17-Dimethyl-2,ll-dithia[3]metacyclo[3](2,4)- thiophenophane 54 2.5.3 Synthesis of £rans-9b 9c-Dimethyl-9b,9c-dihydrophenyleno- [l,9-bc]thiophane, 120 57 2.5.4 The first diatropic bridged thiaannulene 60 2.5.4.1 Introduction 60 2.5.4.2 UV-Vis spectrum of 120 63 2.5.4.3 NMR spectra of the thiaannulene, 120 65 2.5.4.4 A look at vicinal coupling constants, geometries and comparison with other bridged heteroannulenes 70 2.5.4.5 Estimation of diatropicity in the thia[ 13]annulene 120 75 2.5.4.6 Comparison of the diatropicity of 120 w ith other hetero-DMDHPs 81 2.6 A short synthesis of 2,4-bis(bromomethyl)-3-methylthiophene, vi 110 83 2.7 Attempted synthesis of the q uasi-biphenylene 157 86 2.7.1 Introduction 86 2.7.2 Retrosynthetic analyses for 157 86 2.7.3 Synthesis of l,3-bis(methoxymethyl)-2-methylbiphenylene 89 2.7.4 Attempted synthesis of the bis-bromides 159 91 2.8 Thiophene-1,1-dioxides in syntheses 93 2.9 Summary 95 CHAPTER THREE SYNTHESES USING REACTIVE INTERMEDIATES 3.1 Introduction 96 3.2 Syntheses using oxa[17]annulene 98 3.2.1 Synthesis of the biphenylene fused DMDHP, 192 98 3.2.1.1 Structure of the adduct 191 99 3.2.1.2 Attempted dehydration reactions on 191 103 3.2.1.3 Synthesis of tra ils - 14b, 14c-dimethyl- 14b, 14c-dihydrobenzo- [ 1" ,2": 3,4] cyclobuta[ 1,2-b] naphtho [2,1,8 -fgh] anthracene ,192 104 3.2.1.4 Properties of the biphenyleno DMDHP 192 106 3.2.1.5 l3Cnmr spectrum of 192 108 3.2.1.6 'Hnmr spectrum of 192 111 vii 3.2.1.7 Coupling constant-bond order correlations in 192 114 3.2.1.8 Estimation of diatropicity of biphenylene from 192 120 3.2.2 Attempted synthesis of the methanol 10]annuleno- D M D H P 208 125 3.2.2.1 Attempted synthesis of the cydopropabenzo[a]DMDHP 129 3.3 Syntheses using arynes 137 3.4 Summary 140 CHAPTER FOUR SYNTHESES USING CLASSICAL INTERMEDIATES - APPROACHES TO [e]-ANNELATED DMDHPs 4.1 Introduction 141 4.2 Model studies using 2,6-dichlorotoluene 143 4.3 Search for a direct synthesis of 1,2-diketones 147 4.4 A new synthesis of symmetrical 1,2-diketones 149 4.4.1 Synthesis of l,2-bis(3’-methoxymethyl-2’-methylphenyl)- ethanedione, 241 152 4.5 Significance of the diketone synthon 241 154 4.5.1 1,2-Diketones in the synthesis of various aromatic rings 154 4.5.2 Some model ring syntheses using the dione 249 156 4.6 Utility of the 1,2-diketone-synthesis of the quinoxalinodihydropyrene 279 160 viii 4.6.1 Structure of the thiacyclophane 287 162 4.6.2 Synthesis of the dihydropyrene 279 109 4.6.3 'Hmnr spectrum of the dihydropyrene 279 and comparison with the naphtho[e] dihydropyrene 58 171 4.7 Syntheses using thiophene-1,1-dioxide- Formation and some reactions of the thiophenedioxide 296 176 4.8 Barrier to rotation in o-teraryls 181 4.8.1 Introduction 181 4.8.2 Rotational isomersim and experimental estimation 182 4.9 Summary 188 5 CONCLUSIONS 180 6 EXPERIMENTAL 208 REFERENCES 254 APPENDIX 277 ix LIST OF TABLES Table page 1 'Hnmr chemical shifts of selected annulenes. 11 2 REPE (in (3 units) of some selected conjugated compunds 19 3 Calculations of the RE of benzene (kcal/mol) 20 4 RE of some heterocycles from thermochemical data in kcal/mol 23 5 Chemical shifts of internal CH., protons for subtituted DMDHP. 25 7 Predicted and observed internal methyl proton chemical shifts of some fused DMDHPs. 28 8 Comparison of the longest Xm.ix o f 120 and related annulenes 65 9 Chemical shifts of Ha and CH., of seme thiaannulenes. 69 10 Comparison of JA/JB ratios of 141 and related systems 72 11 Comparison of some MM results and JA/JB ratio of 120, 63 and 12 74 12 Coupling constant and bond order data for compound 120 78 13 Comparison of diatropicities of 12, 1L0, 63 and 33, from the chemical shifts of their external and internal protons 82 14 Comparison of 13C chemical shifts of 47, 12, 192 and 49 111 15 C om parison of tc-SCF bond orders and bond orders derived from ,3J’s 116 16 Coupling constant, bond order and chemical shift data for compound 192.
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