The cycloaddition of benzonitrile oxide to 2-alkoxy-5,6- dihyclro-2H-pyrans was investigated with particular interest in the factors affecting the regio- and stereoselectivity of the reaction. The 2-methoxy analogue showed weak activity and little selectivity. The isolated products consisted of two by-products, three 1:1 cycloadducts and three 2:1 cycloadducts. The -butoxy analogue afforded only two cycloadducts. Both arose from attack anti to the bulky alkoxy substituent. Addition of benzonitrile oxide and Q,j-dipheny1njtrone to a bridged pyran, 6,8-dioxabicyclo[3 .2. l]oct-3-ene, showed similar selectivity and much enhanced reactivity. Levoglucosenone, a chiral bicyclic enone showed excellent reactivity and selectivity in reaction with benzonitrile oxide. Two cycloadducts were isolated in a ratio of ca. 100:1 and a combined yield of 71%; the major adduct having added from the face anti to the methyleneoxy bridge. This isoxazoline was investigated further in reactions involving reduction of the carbonyl group, acetal formation and nucleophilic addition of nitromethane. Levoglucosenone was also shown to be a reactive dipolarophjle to other 1,3-dipoles such as nitrones, a nitrile imine and a carbohydrate nitrile oxide. The chemistry of some of these adducts was also investigated. Finally, the Michael addition of nitromethane to levoglucosenone was investigated under many different conditions and with different basic catalysts. The aim was to synthesise levoglucosenone with a primary nitro substituent to use as a nitrile oxide precursor. The series of reactions afforded 8 identifiable products, none of which was the desired Michael adduct.

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Crosslinking of low density polyethylene by ultraviolet light was carried out. The polyethylene was incorporated with high functionality monomer (crosslinking agent) and photoinitiator. Saturated and unsaturated hydrocarbon model systems were used in the project, in order that a better understanding of the crosslinking process could be established. A comparison between photoinitiation crossing and Gamma irradiation process of the model systems and polyethylene was also carried out. It was found that the properties of the photoinitiated crosslinked polyethylene were significantly improved, especially the flow properties and the environmental stress cracking resistance (ESCR). Other properties such as Tensile strength, Glass transition temperature (Tg) and melting temperature (Tm) were not greatly affected. The significant improvement in the flow properties was due to the formation of the microphase of the high functional crosslinking agent which was incorporated in the polyethy.lene matrix. The formation of such a microphase was only achieved within the amorphous region of the polyethylene.

It had always been assumed that electron addition to organic halides resulted in dissociation as in reaction [1]. RX + e- → R. + X- .... [1] In more recent years, intermediate species have been isolated; in particular the R./X- adduct (where R is an alkyl group) and the (R-.X)- o* anion (where R is, for example, the -CF3 group). Chapters 2-5 document the isolation of a range of alkyl radical/ halide ion adducts in a range of matrices. Particularly exemplary results were obtained from the adamantane matrix, Chapter 1 therefore reviews the physical properties of the compound and the chemical methods employed for its purification and for the incorporation of substrates into its lattice. Conversely, Chapters 6 and 7 discuss the theory of formation of o* anions and documents a series of attempts at their isolation. Finally, Chapter 8 probes and compares the thermally and photo-lytically induced [1,2] hydrogen atom shift isomerisation processes of the But. and isoBu. radicals and But./X- and isoBu./X- adducts (X = C1, Br, I) in a range of matrices (reactions [2] and [3]).

published_or_final_version / Chemistry / Doctoral / Doctor of Philosophy

Chapter One describes attempts at utilising ortho-quinodimethanes in the synthesis of polycyclic ring systems, where construction of the the 1,4-elimination precursor could not be achieved. Additionally, several attempts were made to utilise the diradical behaviour which ortho-quinodimethanes are thought to possess, in similar annulative reactions. Unsuccessful attempts at generating furanyl- ,benzofuranyl- and benzenoid- derived diradical species, however, brought these particular studies to an end. The remainder of this thesis is devoted to studies that were made into developing new uses for benzynes in organic synthesis. Their discovery, general history and subsequent application is divided for convenience into three chapters; Chapter Two covers the discovery of these classic species, and approaches to these species which have been improved from the highly impractical methods which were originally developed. Chapters Three and Four give an overall review of the past and recently reported applications of benzynes in organic synthesis; Chapter Three covers the use of benzynes in nucleophilic couplings, whilst Chapter Four covers their application in cycloaddition reactions. Chapter Five describes preliminary studies that were made into developing new routes to polycyclic ring systems via the intramolecular Diels-Alder trapping of benzynes. After unsuccessful attempts at utilising the anthranilic acid route to benzynes, the remainder of the studies were concentrated on utilising the 1-aminobenzotriazole route to benzynes, a mild, efficient, yet relatively underexploited route. An improved synthesis of 7-methyl-1-aminobenzotriazole is described, as is the functionalisation of the methyl substitutent in the BOC-derivative via the formation of the dianion. However, 1,3-diene incorporation via this route was unsuccessful, due to difficulties in preparing suitable l,3-dienes. Chapter Six describes attempts at applying the metallation chemistry of BOC-protected 7-methyl-l-aminobenzotriazole to the synthesis of 2-substituted dihydrobenzofurans (n = 0) and chromans (n = 1) via the intramolecular trapping of benzynes by flanking hydroxyl functions, which were incorporated via the condensation of the dianion with aldehydes and epoxides respectively. Using H-bromosuccinimide as the reagent for benzyne generation, benzo-fused heterocycles were successfully generated in moderate yields, with bromine incorporation also being achieved (X =Br). Using lead (1V) acetate, simple dihydrobenzofurans (X=H) were obtaine4 in better yields. Excellent yields, in some cases virtually quantitative, were obtained using N-iodosuccinimide as the reagent, with the iodine substituent (X = I) being incorporated. The additional bonus of having the iodine substituent was highlighted by utilising iododihydrobenzofurans and chromans in subsequent coupling reactions. Overall, this thesis describes the advances made in increasing the role of benzynes in synthetic organic chemistry, providing novel metalation chemistry on the aminobenzotriazole ring system, and a novel annulative approach to valuable synthetic and potentially active species such as dihydrobenzofurans and chromans. Above all, this work illustrates that under certain suitable conditions, benzynes can serve as extremely efficient reactive intermediates in heterocyclic annulations.

The contents of various exocrine glands from 8 species of bumblebees (representing 5 subgenera) and 16 species of ants (representing 5 subfamilies and 8 genera) have been examined using gas chromatography-mass spectrometry. A close correspondence between the Dufour gland secretions and cuticular hydrocarbon patterns of several bumblebee species has been discovered. However, this similarity was not found to be universal for the Bombus genus. The mandibular gland secretions of two entire colonies of the primitive queenless ant Dinoponera australis have been examined. A blend of tri- and novel tetrasubstituted pyrazines have been identified, and a link has been found between worker function and the total amount of secretion in each individual. An investigation into the chemistry of army ants of the genus Aenictus has led to the first identification of an army ant pheromone. The trail pheromone, produced by postpygidial glands, was determined to consist of a mixture of methyl nicotinate and methyl anthranilate. The short and long-range recruitment pheromones of the closely related ants Aphaenogaster albisetosus and A. cockerelli have been identified as 4-methyl-3-heptanone (80% (S)-, 20% (R)-) and (R)-l-phenylethanol, originating from their respective poison glands. The recruitment pheromones of Pogonomyrmex barbatus, P. maricopa, P. occidentalis and P. rugosus have been identified as a mixture of 2,5-dimethylpyrazine, trimethylpyrazine and 3-ethyl-2,5-dimethylpyrazine.

The work presented in this thesis describes several new and novel radical macrocyclisation-transannulation cascade reactions directed towards the single step construction of ring-D aromatic steroid ring systems. The introduction introduces the steroid class of natural products, their biosynthesis and previous literature strategies towards their construction. The ring-D aromatic steroids, together with their possible total synthesis via a novel freeradical cascade strategy, are then discussed. The results and discussion chapter summarises the radical cascade strategies towards ring-D aromatic steroid ring systems that have been investigated. It is divided into two sections: Part 1 describes the evolution of our current radical cascade approaches relating to the iododienynone precursors 117a-d (Schemes 26-29). We proposed that the precursors 117a-d would lead to the 6,6,6,6 ring-D aromatic steroid ring system (such as that found in the natural product nicandrenone 67), via a cascade of radical ring-forming reactions. However, the proposed radical cascade from the Z-iododienynones 117a,c halted at the macrocyclisation stage producing the macrocycles 137a,b, whilst a radical cascade from the E-iododienynones 117b,d instead led to the unusual bridged tricyclic structures 148a,b and 155 (depending on whether benzene or heptane was used as the solvent), rather than the anticipated linear tetracycles 116a,b. A rationale for these outcomes is given. Part 2 discusses an approach to 6,6,5,6 ring-D aromatic steroids via a macrocyclisation-transannulation radical cascade from the vinylcyclopropyl seleno ester precursor 193. A synthesis of the radical precursor 193 was first examined using a novel aryl-vinylcyclopropane Stille reaction coupling protocol (the development of which is discussed), as well as several alternative routes. A practical, albeit more lengthy, synthesis of the precursor 193, was then developed. The proposed radical cascade from the vinylcyclopropyl seleno ester 193 led to the desired ring-D aromatic steroid ring system 194a (with the correct trans, anti, trans stereochemistry) together with the methyl epimer 194b. Also isolated from the product mixture was the macrocycle 232, together with the products of reduction and decarbonylation of the acyl radical intermediate 235, i.e. 231 and 230, and the dioxolane 233. The experimental section describes all the procedures used to synthesise the precursor compounds 117a-d and 193 and the products of their radical mediated cascade cyclisations. Full NMR, and other spectroscopic data, alongside mass spectrometry data are also given. The appendices include some relevant X-ray and NMR spectroscopic details.