No description available.

No description available.

I. Diels-Alder reactions of 1,2,3,4,9,9-hexachloro-1,4,4a,8a-tetrahydro-1,4-metha- nonaphthalene (16) and 1,2,3,4,9,9-hexachloro-1,4,6,7-tetrahydro-1,4-methanonaphthalene (17) toward dienophiles N-methyl-1,2,4-triazoline-3,5-dione (MTAD), N-phenyl-1,2,4-triazoline-3,5-dione (PTAD) and/or N-methylmaleimide (NMM) have been examined. II. Epoxides derived from functionalized 1,4,4a,9a-tetrahydro-9,10-dioxo-1,4-methanoanthracenes (1a and 1b) undergo acid- and base-promoted intramolecular nucleophilic ring-opening to form new polycyclic alcohols. III. The title cycloalkylidenecarbene has been generated via reaction of 8-methylenepentacyclo[5.4.0.0^{2,6}.0^{3,10}. 0^{5.9}]undecan-11-one (44) with diethyl diazomethyl-phosphonate (DAMP). This species could be trapped in situ by cyclohexene, thereby affording the corresponding cycloadduct 46a and 46b.

Large scale chemical reaction networks are a ubiquitous phenomenon, from the metabolism of living cells to processes in planetary atmospheres and chemical technology. At least some of these networks exhibit distinctive global features such as the “small world” behavior. The systematic study of such properties, however, suffers from substantial sampling biases in the few networks that are known in detail. A computational model for generating them is therefore required. Here we present a Toy Model that provides a consistent framework in which generic properties of extensive chemical reaction networks can be explored in detail and that at the same time preserves the “look-and-feel” of chemistry:  Molecules are represented as labeled graphs, i.e., by their structural formulas; their basic properties are derived by a caricature version of the Extended Hückel MO theory that operates directly on the graphs; chemical reaction mechanisms are implemented as graph rewriting rules acting on the structural formulas; reactivities and selectivities are modeled by a variant of the Frontier Molecular Orbital Theory based on the Extended Hückel scheme. The approach is illustrated for two types of reaction networks:  Diels−Alder reactions and the formose reaction implicated in prebiotic sugar synthesis.

No / Phosphonium tosylates have been investigated as solvents for the Diels¿Alder reactions of isoprene with methyl acrylate, but-3-en-2-one and acrylonitrile. The reactions with oxygen-containing dienophiles showed high regioselectivity. Graphic

This thesis describes synthetic studies towards the tricyclic terpene framework of the cytotoxic natural product eleutherobin, and the investigation of biocatalytic methodology towards late stage functionalisation of the structure. Chapter 1 provides an introduction to the biomedical significance of the natural product and to the various synthetic studies reported to date. Chapter 2 explores intramolecular Diels-Alder approaches to the construction of the nine- and six- membered rings present in the natural product. Chapter 3 describes alternative approaches to the eleutherobin core structure, leading to a formal synthesis of the natural product. The synthetic sequence developed is applied to the preparation of a small library of furanoid analogues of eleutherobin. Chapter 4 details the development of methodology for the one-pot preparation of (E)-4-methylhexa-3,5-dien-1-ol, and its use in an intermolecular Diels-Alder/lactonisation sequence to achieve enantioselective preparation of an important lactone building block. Chapter 5 describes studies on the mP450-mediated oxidation of various eleuthoside structures obtained. Finally, Chapter 6 details the construction of an electrochemical flow cell, and its use for the anodic oxidation of furfuryl alcohol derivatives.

he thesis entitled "Theoretical Studies of pie-Facial Selectivity in Organic Reactions" involve a computational examination of a suitable reactivity problem in organic chemistry. Systematic and efficient -procedures have been developed and tested for rationalizing observed face selectivities in numerous substrates. In a number of cases precise transition state structures have also been computed in a rigorous manner. The molecules examined are by and large sterically unbiased. Considerable emphasis has been placed on obtaining general interpretations, In particular, the relative contributions of various sterio electronic and electrostatic effect have been considered in detail.Predictions of a-face selectivities haw also been made in a few cases. In recent years many mildly perturbed substrates have been shown to undergo pie-face selective reactions. Chapter 1 provides a brief review of the available experimental result involving nucleophilic, electrophilic, radical and Diels- Alder reactions.The current status of theoretical understanding of theae rasults is also summarized.The discussion includes qualitative proposal as well as quantitative calculations on selected substrates. The principal goals of the present work and general features of the MO methods used are briefly discussed.

In chapter I Photo-retro-Diels-Alder (PrDA) reactions of a variety of Diels Alder (DA) adducts were studied. Experimental results showed that the photoreactivity (quantum yield) depends on the electron-donating ability of the diene component and the electronwithdrawing ability of the dienophile component. The mechanism was studied by trapping the reaction intermediate, O2 quenching and femtosecond time-resolved absorption spectroscopy. All the results support a mechanism that involves a charge-separated intermediate generated from a singlet excited state. The PrDA reaction may find applications in photoresponsive materials, photolithography, drug delivery and mechanistic research. Chapter II shows two applications of the PrDA reaction. The first, being the formation of the 2 nd -ring DA adduct together with the central-ring adduct in a reaction of pentacene and tetracyanoethylene (TCNE) at room temperature. DFT calculations showed that the difference between the free energy of the two isomers is about 3.9 kcal/mol. Photo- and thermally induced isomerization between the central-ring adduct and the 2nd -ring adduct were studied in solutions and in polymer films. In solution, the less stable 2nd -ring adduct can be completely converted to the more stable central-ring adduct either thermally or photochemically, but the reverse transformation does not occur. In a polymer matrix, isomerization can be photochemically induced in both directions at different wavelengths, which results in a photoswitchable system. Formation of pentacene in the photochemical experiments was also observed, which supports an isomerization process involving a photoretro-Diels Alder (PrDA) reaction. iv The second application was the design and synthesis of a polymer with an anthracene diketone moeity which could undergo a PrDA reaction which should result in significant conductivity changes. Although the synthesis of this type of polymer was unsuccessful during this study, we still believe in the theoretical soundness of the synthesis and utility of this type of polymer. Chapter IV undertakes the study of a class of photoacids which are based on a merocyanine core. These photoacids have been studied and characterized using UV-Vis spectroscopy and the pH of two photoacids have been shown to decrease by 2.0 units upon irradiation with blue light. In addition, the relaxation times of these photoacids have been studied in water and ethanol. We have taken one step further and synthesized and characterized three polymers which have a photoacid moeity in them. These polymers respond to visible light reversibly in solution and in solid state.

No description available.

No description available.