Synthetic and Conformational Studies of Cyclic Systems

Cuthbertson, Eric (1974) Synthetic and Conformational Studies of Cyclic Systems. PhD thesis, University of Glasgow.

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Part I begins with a literature survey on the conformations of unfused seven-membered ring systems. The preparation of a series of seven-membered heterocycles containing a cis-azine grouping is then described. The reaction of a hindered diketosulphide with hydrazine led to the expected 2,7-dihydro-1,4,5-thiadiazepine or several other products one of which contains the novel 8-oxa-3-thia-6,7-diazabicyclo[3.2.1] octane ring system. The crystal-structure and reactivity of this compound are discussed. The determination, by the kinetic 1H n. m. r. method, of the barriers to ring-inversion in the cyclic azines is then described, values between 12.1 and 21.1 kcal/ mole being found. The likely conformational equilibrium, and the electronic and steric effects influencing the relative magnitudes of the barriers, are considered. The free-energy barrier for eucarvone is found to be consistent with the greater conformational mobility expected for seven-merabered carbocyclic 1,3-dienes. A few other related kinetic n. m. r. studies are also reported. In Part II, after a review of the preparation and synthetic applications of 9-heterobicyclo[3.3.1] nonane derivatives, studies of the reactions of syn-3,7-dibromo-cis,cis-cycloocta-1,5-diene are described. These include routes to dioxaadamantane and to several 9-heterobicyclo[3.3.1]nona-2,6-dienes, as well as a [3.3.1] carbocycle. The formation of the fluxional bicyclo[5.1.0]octa-2,5-diene by three different routes was discovered, including tellurium extrusion from 9-tellurabicyclo[3.3.1]nona-2,6-diene; pyrolysis of other cyclic tellurides was also studied. Attempts to prepare bicyclo[3.3.2] and [3.3.3] systems from the dibromo-cyclooctadiene were unsuccessful, but in two cases, the novel 8,10-dithiabicyclo[5.3.1]undeca-2,5-diene ring system was formed by a rearrangement. The final sections describe: studies of the mass spectral fragmentation of some 9-heterobicyelo[3.3.1] nona-2,6-dienes, 1H n. m. r. studies of such systems and their conformational implications, and lastly, 1H n. m. r. studies of the 8,10-dithiabicyclo[5.3.1] undeca-2,5-diene system, from which its preferred conformation in solution is deduced.

Item Type: Thesis (PhD)
Qualification Level: Doctoral
Keywords: Organic chemistry
Date of Award: 1974
Depositing User: Enlighten Team
Unique ID: glathesis:1974-78673
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 30 Jan 2020 15:04
Last Modified: 30 Jan 2020 15:04

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