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The Synthesis and Reactivity Of THE SYNTHESIS AND REACTIVITY OF 3,7 1,3 TETRACYCLO ^3.3.1.1 .0 J DECANE by EDWARD JOHN THORPE B.Sc. (Hons.) University of British Columbia, 1965 M.Sc. University of British Columbia, I968 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF' THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY in the Department of Chemistry We accept this thesis as conforming to the required standard THE UNIVERSITY OF BRITISH COLUMBIA August, 1975 In presenting this thesis in partial fulfilment of the requirements for an advanced degree at the University of British Columbia, I agree that the Library shall make it freely available for reference and study. I further agree that permission for extensive copying of this thesis for scholarly purposes may be granted by the Head of my Department or by his representatives. It is understood that copying or publication of this thesis for financial gain shall not be allowed without my written permission. Department of The University of British Columbia Vancouver 8. Canada Date it, H-u^jf IVi I - ii - ABSTRACT Supervisor: Dr. R. E. Pincock The structures and some properties of adamantane (lb), strained cyclopropanes (23), and certain small ring propeller• like molecules (28) are reviewed. The synthesis of a new type of compound containing a combination of such structures and properties is presented. This compound tetracyclo more simply 1,3-dehydroadamantane (DHA) contains a very strained cyclopropyl group within an adamantane skeleton and was produced by bonding two bridge• head (tertiary) carbons together across the normally extremely rigid structure of adamantane. (This new compound, DHA, is shown below.) In the synthesis of DHA using alkali metal (or alloys) with 1,3-dibromoadamantane (37)> the reaction times and relative yields of adamantane and DHA were extremely variable. The former difficulty was resolved - iii - by the addition of an initiator (usually t_-butyl alcohol), while the yields were increased and made consistent by substituting sodium naphthalide or n-butyl lithium - hexamethylphosphoramide for the alkali metals. DHA and adamantane were also isolated as the major products from the reaction of 1,3,5-tri- and 1,3,5,7-tetrabromoadamantane with alkali metals or alloys. DHA is one of the few organic molecules which possesses a so-called inverted geometry about the internally bonded bridgehead (quaternary) carbons. Wiberg, Hiatt and 55 Burgmaier have defined an inverted carbon as one "in which all atoms joined to the bridgehead atoms (inverted carbons) lie in one hemisphere, (i.e. in one plane or on one side of a plane passing through the bridgehead atoms)." The inversion of the DHA bridgehead carbons results in a highly strained bond and an unusually great reactivity for a formally saturated hydrocarbon. DHA reacts spontaneously with oxygen at room temperature to give a peroxy polymer Ad - 0 -f 0 - Ad - 0 OAd which explodes at o X ca. 1A-6 C. DHA also reacts rapidly with halogens, acids, and mercuric acetate to yield halides, esters and alcohols, respectively. Although the direct reaction of DHA with - iv - alcohols is slow (more than Zl\ hr to complete), Lev/is acid catalysts promoted rapid addition of both alcohols (to give ethers) and benzene (to give phenylated adamantanes). Adam's catalyst promoted the rapid (30 min) addition of hydrogen to DHA in n-heptane solution to produce adamantane. o In the solid phase DHA polymerized readily at ca. 160 C to give a highly insoluble product, polyadamantane Ad-(Ad) -Ad which possesses great thermal stability (decomposition point ca. 500° C under nitrogen). In n-octane solution under nitrogen the half life of DHA was if,45 hr at 195 °C, The reaction of DHA with halogens in ether gives (3-halo-l-adamantanyl)-diethyl oxonium trihalide. The reaction of this unstable intermediate with nucleophiles, for example H2O or NaCN, is discussed as a potential source of unsym- metrical 1,3-disubstituted adamantane derivatives. 1 - V - TABLE OF CONTENTS Page INTRODUCTION 1 A. Adamantane 2 B. Cyclopropanes and Small Ring Propellanes 16 C. Adamantane Molecules containing Cyclopropyl Bonds 23 RESULTS 28 A. Preparation of Brominated Adamantanes 28 B. Preparation of 1,3-Dehydroadamantane 30 C. Structure of 1,3-Dehydroadamantane 32 D. Reactions of 1,3-Dehydroadamantane 33 DISCUSSION 46 A. Synthesis i+6 , B. Structure of 1,3-Dehydroadamantane 59 C. Reactions of 1,3-Dehydroadamantane 68 D. Conclusions 103 EXPERIMENTAL 105 A. Preparation of Brominated Adamantanes 109 B. Preparation of 1,3-Dehydroadamantane - Representative Reactions llif C. Reactions of 1,3-Dehydroadamantane 129 BIBLIOGRAPHY 161 - vi - LIST OF TABLES Table Page I Representative Syntheses of 1,3- 55 Dehydroadamantane II Microanalytic Results for the Intermediate 75 Compound Formed from 1,3-Dehydroadamantane v/ith Bromine in Ether III Substitution of (3-Bromo-l-adamantanyl)- 82 diethyloxonium tribromide with Nucleophiles IV Substitution of (3-Bromo-l-adamantanyl)- 82, 141 diethyl oxonium tribromide in Solvent Mixtures V Normalized 1,3-Dehydroadamantane Trace 160 Weights for Samples after Various Times at 195°C - vii - LIST OF FIGURES Figure Page 1. The NMR Spectrum of 1,3-Dehydroadamantane in Benzene at 100 Mcps 60 2. The NMR Spectrum of 3,7-Dimethy1-1,3- dehydroadamantane in Benzene at 100 Mcps 61 3. The NMR Spectrum of (3-Bromo-l-adaraantanyl)- diethyl oxonium tribromide in Acetone-d,- at 100 Mcps "D 77 k. The NMR'Spectrum of l-Bromo-3-ethoxyadaman- tane in CDCl^ at 100 Mcps 78 5. The NMR Spectrum of l-Bromo-3-hydroxy- adamantane in CDCl^ at 100 Mcps 81 - viii - ACKNOWLEDGEMENTS I would like to express my sincere gratitude to Dr. R. E. Pincock for his patient and continual help during the course of this v/ork. I would also like to thank Dr. R. Stewart, Dr. D. E. McGreer and Dr. E. Piers for their helpful suggestions and comments. I dedicate this thesis to my long suffering wife, Bonnie, without whose encouragement and assistance this thesis would not have been finished. INTRODUCTION This thesis reports a study of the synthesis and reactions of the compound tetracyclo j~3.3.1.1^'^.O^'^ decane (la) or more simply 1,3-dehydroadaraantane (DHA). This compound can be viewed both as a modified adamantane compound and as a strained cyclopropane compound. Thus, the introduction to this work is divided into three sections. The first section describes adamantane, its synthesis and properties. The second section briefly relates the development of the theory of the cyclopropyl bond and the alteration in the properties of this bond when other small ring groups are fused with the cyclopropane molecule. The final section reviews those adamantane derived compounds which contain cyclopropyl groups and are therefore closely related to 1,3-dehydroadamantane (DHA). - 2 - A. Adamantane Adaraantane is the common name for the roughly 2 3 7 spherical or globular molecule, tricyclo 3.3.1.3 ' decane (lb). Diagram 1 Two dimensional representations of adamantane do not do justice to the high symmetry of this molecular structure. The molecule possesses a tetrahedral symmetry identical with the bonding orbitals of a sp3 hybridized carbon atom. This symmetry can be verified by drawing imaginary planes through each of the four cyclohexane rings so that these planes pass through the tertiary carbon atoms to form an imaginary tetrahedron with each of the bridging or tertiary carbon atoms at a vertex. Theoretically, an adamantane compound with four different bridgehead substitutents should be resolvable into optically active isomers. Firstly, Hamill and McKervey have synthesized the analogue or adamantalogue (2a) of lactic acid (2b). They have shown that the bromination product (2a) does indeed possess a small but measurable increment of optical activity.- - 3 - Diagram 2 The structure of the optically active adamantalogue (2a) was confirmed by treatment with sodium hydroxide solution. The product (2c) was identical with a product obtained from an unrelated unambiguous synthesis. Finally, Stetter, Bander and Neumann-^ have observed and studied a vicinal dichloro-allene (2a) type of optical isomerism in the following adamantalogue (2b). a b Diagram 3 Rearrangements enlarging or breaking the adamantane r skeleton have been reported with increasing frequency despite the generally acknowledged thermodynamic stability of this skeleton.7 F' - 4 - By further pursuing the analogy between the tetra- hedrally hybridized carbon atom and adamantane, several groups have synthesized adamantalogues of simple aliphatic hydrocarbons. To date, the adamantalogues for ethane, methane and propane have been synthesized. The synthesis 8a of higher hydrocarbon adamantalogues remains under study. Neither the high symmetry nor the related high thermodynamic stability' of adamantane was utilized in the early syntheses and studies of the compound. The yields of these syntheses were poor. Despite their low yields, these total syntheses were important because they were the only source of secondary and tertiary substituted adamantane derivatives. The importance of these synthetic routes did not diminish substantially after Stetter and V/ulf^ developed a method for progressively increased bridgehead substitution of adamantane. The symmetry of adamantane made dissimilar substitution difficult to achieve by the Stetter and Wulf approach. Early efforts to synthesize adamantane were stimulated v/hen it was realized that the sole source of this interest• ing compound was controlled by a strong monopoly which released it only in minute amounts. Since its discovery in the petroleum from the Hodinin fields of Czechoslovakia, only very small amounts of the compound found their way out of Landa's laboratory.To correct this artificial - 5 - scarcity many attempts were made to synthesize adamantane. 11 The first attempt on record is attributed to Meerwein (4). R=C02Me CH20+CH2(C02CH3 )2 R Diagram k Kleinfeller and Frercks.1 2 attempted two entirely different approaches to the problem both of which also failed (5). N02C(CH2Cl)3 + | • H 3(Et02C )CH2C Diagram 5 - 6 - Bottiger13 was the first to successfully synthesize the adamantane skeleton (6), however, adamantane itself was not realized.
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