<p>Cyclopropanes and carbohydrates are materials of great interest to chemists. Ring opening reactions of cyclopropanated carbohydrates have excellent potential for synthesis, due to the many diverse structures that may be obtained. The work described in this thesis explores the scope of such ring opening reactions, and extends to the synthesis and reactions of several novel cyclopropanated carbohydrates, in which synthesis of a natural product was also investigated. Several bicyclic gem-dihalocyclopropanes, including 97, were synthesised. Base-mediated cyclopropane ring opening of 97 in the presence of nucleophiles afforded a series of 2-C-branched glycosides 389 and 390 (Chapter 2), whereas silver-promoted ring expansion provided access to seven-membered rings (255 and 256) (Chapter 3). Studies on the mechanisms of the ring opening processes were also carried out. Ring-opening reactions of carbohydrate-derived gem-dihalocyclopropanes were also applied to the exploration of possible routes to the natural product (--)-TAN-2483B (154). Attempts to convert d-galactose and d-xylose into the dihydropyran 193 are the subject of Chapter 4, while the transformation of d-mannose into 193 and subsequent efforts to prepare the natural product 154 are discussed in Chapter 5.</p>
<p>Cyclopropanes and carbohydrates are materials of great interest to chemists. Ring opening reactions of cyclopropanated carbohydrates have excellent potential for synthesis, due to the many diverse structures that may be obtained. The work described in this thesis explores the scope of such ring opening reactions, and extends to the synthesis and reactions of several novel cyclopropanated carbohydrates, in which synthesis of a natural product was also investigated. Several bicyclic gem-dihalocyclopropanes, including 97, were synthesised. Base-mediated cyclopropane ring opening of 97 in the presence of nucleophiles afforded a series of 2-C-branched glycosides 389 and 390 (Chapter 2), whereas silver-promoted ring expansion provided access to seven-membered rings (255 and 256) (Chapter 3). Studies on the mechanisms of the ring opening processes were also carried out. Ring-opening reactions of carbohydrate-derived gem-dihalocyclopropanes were also applied to the exploration of possible routes to the natural product (--)-TAN-2483B (154). Attempts to convert d-galactose and d-xylose into the dihydropyran 193 are the subject of Chapter 4, while the transformation of d-mannose into 193 and subsequent efforts to prepare the natural product 154 are discussed in Chapter 5.</p>
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The synthesis of the A-B bicyclic ring structure 3 of the natural product Stemocurtisine is described. The synthesis was accomplished in seven synthetic steps from commercially available L-glutamic acid. The key step involved a borono-Mannich reaction between the hemiaminal 6 and trans-β-styryl boronic acid and trans-β-styrylpotassiumtrifluoroborate to prepare the cis diene 4. Attempts to prepare the A-B-C ring compound 2 via intramolecular epoxide ring opening followed by rearangement under different basic conditions were unsuccessful. Only unreactive starting material was recovered.
Tetraalkyl cyclobutene-1,2,3,4-tetracarboxylates, prepared by intramolecular Wittig reaction between a vinylphosphonium salt and diethyl 2-oxobutanedioate, undergo electrocyclic ring-opening reactions, in boiling toluene, to produce highly electron-deficient 1,3-dienes.
Investigations of Ring-Opening Reactions of Cyclopropanated Carbohydrates: Towards the Synthesis of the Natural Product (--)-TAN-2483B
