The interplay of structure and reactivity on a ring closing metathesis reaction

This Thesis describes investigations of how structure affects a cyclooctannulation of a difluorinated diene via ruthenium-catalysed ring closing metathesis (RCM). The study originated in attempts to optimise these reactions towards the synthesis of novel difluorinated analogues of sugars.;A range of difluorinated dienes have been synthesised in order to study the effects of allylic protecting group on cyclisation efficiency, using the CF2 group as a probe to reaction outcomes via 19F NMR. We identified a 102 fold difference in cyclisation efficiency depending on which allylic protecting group was used. However, kinetic studies have shown us that allylic protecting groups have only a moderate effect on cyclisation rate. Kinetic studies have also shown us that the cyclisation is affected by the presence of gem-dialkyl groups, which accelerate the rate---an effect which has not been quantified for the formation of medium rings by RCM previously.;1H NMR kinetics has enabled the identification of the most significant catalytic species on the reaction timescale, including identification of catalytic decomposition products. This has led to the development of a kinetic data model to which all kinetic data were fitted, using simulation software, and has allowed a deeper analysis and understanding of how olefin structure affects reactivity in RCM.;Based on the kinetic data, RCM substrates, which prolong catalytic lifetime and simplify reaction kinetics have been synthesised and examined. In addition to this, the effects of reaction solvent, temperature, catalyst and catalyst loading on the cyclisation rate have been studied in order to identify the optimum conditions for synthesis of the desired difluorinated cyclooctenones.