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The work is based on pseudorotaxane formation between different hosts and guests employing noncovalent interactions and investigating their disassembly using various external stimuli. Different tools were used to detect the pseudorataxane formation including ID and 2D NMR spectroscopy, UV-Vis spectroscopy, EPR spectroscopy, isothermal titration calorimetry, X-ray crystallography and cyclic voltammetry. A pseudorotaxane was prepared between biologically important cyclodextrin and a tetrathiafulvalene derivative which dissociated upon using a competitive guest for the cyclodextrin. Pseudorotaxane phenomena were extended to the solid-liquid interface by creating a pseudorotaxane architecture on a gold nanoparticle and in another attempt it was engineered at the periphery of a dendrimer. In both instances pseudorotaxanes were formed between 1,5-dialkoxynaphthalene and cyclobis(paraquat-p-phenylene). Atom transfer radical polymerization was used to prepare a living polymer with a naphthalene unit at one end which has the propensity to undergo pseudorotaxane formation with cyclobis(paraquat-p-phenylene). With the aim to create a multicomponent pseudorotaxane the host cyclobis(paraquat-4,4'-biphenylene) was employed which yielded a [3]pseudorotaxane with tetrathiafulvalene. A less conformationally restricted diaminopyridine based model system with different substituents was synthesised which had the ability to sustain hydrogen bonding interactions with flavin in order to understand substituent effects on flavin. electrochemical properties. An axle was synthesised for a pseudorotaxane with a flavin at one end and naphthalene unit at other end. The movements shown by pseudorotaxane association/dissociation bears similarities to molecular machine type movements in which these systems will serve as prototypes in order to create nanoscale molecular machines.

A range of enantiomerically pure iodine compounds has been synthesised and either oxidised to the corresponding hypervalent iodine compound and used as oxidant or employed as catalysts in a range of reactions together with different oxidants in stoichiometric amounts in order to form the respective hypervalent iodine species in situ. Three different enantioselective catalytic reactions have been investigated: cc-acetoxylation of ketones, halolactonisation of pentenoic acids and oc-oxytosylation of ketones. Also - probably for the first time - alkyliodides have been employed as catalysts in these transformations.

This thesis describes different strategies to desymmetrise 1,4-cyclohexadiene derivatives with concomitant formation of a quaternary stereogenic centre. Chapter 1 gives a brief overview of the previous desymmetrisation and diastereotopic group selection processes of 1,4-cyclohexadiene derivatives. Chapter 2 describes the initial model studies for the formation of the quaternary stereogenic centre using achiral cyclohexa-1,4-dienone derivatives. This was developed to permit stereoselective formation of a quaternary stereogenic centre using a chiral sulfinyl group as the stereodirecting influence during the cyclisation step. This proceeded with acceptable levels of discrimination between the two diastereotopic double bonds. Chapter 3 outlines attempts to improve the level of diastereoselectivity obtained under the influence of the sulfinyl group by synthesising a range of different compounds having only carbon atoms in the tether. Chapter 4 describes the desymmetrisation of the two diastereotopic double bonds of derivatives of cyclohexa-1,4-diene using free-radical methodology. The sense and level of the diastereoselectivity is dependent on the protecting group used. Application of this methodology toward natural product synthesis has been described. Chapters 5 describes the desymmetrisation of the two diastereotopic double bonds of 1,4-cyclohexadiene derivatives using the Prins cyclisation reaction. This approach afforded an easy and stereocontrolled access to fused tetrahydropyrans and tetrahydrofurans depending on the reaction conditions employed. The stereochemical outcome of all of these reactions can be rationalised by a single transition state model.

FR901483 was to be synthesised to highlight the applicability of the acid-catalysed hydroamination reaction to natural product synthesis.&nbsp; FR901483 contains a <italic>spiro</italic>-centre, analogues of which have been successfully synthesised in the Knight group.&nbsp; A model study showed that the cyclisation should indeed be possible.

The interactions of certain aromatic nitre compounds with nucleophiles in protic solvents and in protic dipolar aprotic solvent mixtures have been investigated using the techniques of proton magentic resonance and visible spectroscopy. Picrate ion reacts with concentrated aqueous sodium sulphite to give an unusual ion carrying five negative charges. This results from the covalent addition of two sulphite molecules to the picrate ion, at ring carbon carrying hydrogen. At low sulphite concentration a 1:1 adduct is produced. The equilibrium constants for the formation of these complexes have been determined. Solvent effects on the formation of 1:1 adduct were examined in water-dimethyl sulphoxide mixtures. With hydroxide ion in aqueous solutions, the major of the picrate ion is to give a 1:2 adduct.1,2,3,5-Tetranitrobenzene reacts with hydroxide ion or sulphite ion in water, or ethoxide ion in ethanol to form red complexes whose NMR spectra indicate covalent addition of the nucleophile at C(_4). The complexes are not stable and replacement of the nitro group at occurs quickly. The equilibrium and the rate constants for these processes have been measured. In contrast 1,2,4 ,5-tetranitrobenzene reacts with hydroxide ion to give 2,4,5-trinitrophenol without the production of colour. With ethoxide or sulphite ions coloured species are produced. l,3-Dimethoxy-4,6-dinitrobenzene reacts with methoxide ion in dimethyl sulphoxide-methanol mixtures to form an adduct whose NMR spectrum indicates methoxide addition at C(_2). The equilibrium constants in various solvent compositions have been determined. Solvent effects on the stability of Meisenheimer complexes formed from 1,3,5-trinitrobenzene and thiolate ions have been investigated in alcohol-water mixtures. The equilibrium constants for formation of the1:1 adducts are smaller in water than in alcohol but go through a maximum at about 80% alcohol. The equilibrium constants of the 1:2 adducts increase monotonically as the proportion of water is increased and are ca. 10(^3) greater in water than in pure alcohol. This greater stability is attributed partly to the good solvation by water of a localised negative charge on the nitro group between the positions of addition.

The synthesis, isolation and characterisation of aryl and heteroarylbutadiynes is herein reported. X-ray structural analysis for terminal butadiynes 72,118, 143, 157, 162 and 172 has been obtained. The packing diagrams indicate, in most cases, a hydrogen bonding interaction between the terminal acetylenie proton and the appropriate atom in the ring. An important feature of our synthetic methodology is the use of the 2-hydroxy-2-propyl protecting group, which facilitates purification from protected species, due to a large difference in polarity. The synthesis of mono- and di-deprotected bis-butadiynes is also reported; indeed X- ray structural analysis of di-deprotected pyridyl bis-butadiyne 234 has been obtained, as shown in the figure below The reactions of aryl and heteorarylbutadiynes and bis-butadiynes have also been investigated, leading to the synthesis of molecular-wire precursors 262 and 264.

My Ph.D research is mainly based on ‘calixarene and coordination complex hosts for anion’. The research is to make synthetic chloride ion channels for possible treatment of cystic fibrosis. Our approach is based on derivatives of larger calix[n]arenes. Calixarenes are chalice-shaped molecules that form readily under base catalyzed-condensation of tert-butyl phenol with formaldehyde. We have synthesized calixarenes which were tuned at the lower rim with bromo alkyl nitrile and reduced followed by reaction with a series of different isocyanates bearing fluorescent functional groups capable of binding and sensing chloride and nitrate. We are also interested how the host ligand binds with metal anions in solution and solid state chemistry. We synthesised simple pyridyl urea ligands and isomorphs. Their anion binding studies are discussed in terms of solid state and solution chemistry. Solid state structures based on silver and copper metal forming contact ion pairs with series of anions like nitrate, chloride, bromide, trifluoroacetate and boron tetrafluoride. Their solution based anion binding studies were performed and control titration results show that these hosts bind anions in a one to one fashion which was confirmed with solid state structures. An interesting aspect is that 2-ureidopyridine ligand exists in four different anhydrous crystal forms (I – IV0), which can be crystallized by several techniques. It was found that forms I and II only crystallize without another polymorph from methanol solution or in presence of inorganic salts. Thermoanalysis shows that all the modifications melt without previous transition and applying the heat of fusion rule proves this system to be completely monotropic. The crystal structures show that the molecule forms one intramolecular and two intermolecular hydrogen bonds to give S(6) and dimeric R (8) graph synthons in all four structures. However packing arrangements differ strikingly and since the hydrogen-bonding arrangement is the same for all the four forms, the differences in energy measured by thermoanalytical methods can only be caused by the different packing arrangements involving combinations of the weaker interactions, with the CH.¼S contacts being among the obvious differences. Thus, this system is a clear example in which the presence of robust, reproducible hydrogen bonded synthons does not lead to any control or predictability of polymorphic form.

Whilst silenes have long been studied for their unique chemistry there has been little attempt to exploit this in other synthetic strategies. As part of a programme to explore this aspect the reactions of readily accessible silenes with alkenes and dienes were studied. Silenes, generated by the thermolysis of acylpolysilanes, add to α,β-unsaturated esters to form silacyclobutanes and silyl-substituted cyclopropanes in moderate yields. Upon silicon-carbon bond oxidation the cyclopropanes were converted directly to 1,4-dicarbonyl compounds, thus demonstrating the formal acyl anion chemistry of acylpolysilanes. In an alternative approach towards milder silene generation, the potential of α-silyl diazo carbonyl compounds was examined. It was found that α-silyl diazo esters undergo rhodium (II) catalysed decomposition to provide short-lived silenes. These intermediates rearrange to oxasilates which can be trapped with α,β-unsaturated ketones. The resulting products contain a high degree of functionality which offers considerable potential for further synthetic transformations. Finally, more complex skeletons were approached through an exploration of intramolecular silene cycloaddition. In this respect, it was shown that thermolysis of acylpolysilanes at 180 oC produced [4+2] cycloadducts, while [2+2] cycloadducts and ‘ene’ products were not observed. Similarly, it was found that intramolecular cycloadducts can be generated at lower temperatures by the addition of MeLi•LiBr to acylpolysilanes. These two approaches allowed the cycloadducts to be synthesised in good yields and moderate diastereoselectivities.

Pyrene derivatives have found use in a wide range of applications that make use of the unique structural, optical and charge-transfer properties of pyrene. Nearly all pyrene derivatives are substituted at the 1-, 3-, 6- and 8-positions, i.e. the sites of electrophilic aromatic substitution. In contrast, derivatives substituted at the 2- and 2,7-postions of pyrene are rare, as their syntheses involve laborious multistep processes. Such derivatives are of interest because they retain the long axis of symmetry and display unusual photophysical properties. Using the regiospecific direct C-H borylation of pyrene with an Ir-based catalyst, prepared in situ via reaction of [Ir(OMe)COD]2 with 4,4’-di-tert-butyl-2,2’-bipyridine, 2,7-bis(Bpin)pyrene 1 and 2-(Bpin)pyrene 2 (pin = OCMe2CMe2O) were synthesized. Straightforward derivatization strategies, converted 1 and 2 into nominally nucleophilic and electrophilic pyrene derivatives, which were further utilized in Suzuki-Miyaura, Sonogashira, Buchwald-Hartwig and Negishi cross-coupling reactions. Using this methodology, a library of 2- and 2,7-substituted pyrenes bearing donor and acceptor groups, including aryl, ethynyl, arylethynyl, alkyl, hydroxy, alkoxy, diarylamino, carboxylic acid and diarylboryl derivatives, was prepared. The solid-state structures of several derivatives obtained by single-crystal X-ray diffraction revealed a diverse range of structures and packing modes. The influence of the substitution position and the nature of the substituent upon pyrene was investigated in a detailed photophysical study. The existence of nodal planes passing through the 2- and 7-positions, perpendicular to the molecular plane, in both the HOMO and LUMO of pyrene accounts for the differing photophysical behaviour of derivatives substituted at 2- and 2,7-positions from those substituted at the 1-position. Finally, the applicability of iridium-catalysed C-H borylation and metal-catalyzed cross-coupling is further demonstrated on a range of interesting substrates.