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Title: 1,3-Dipolar cycloaddition reactions of triene-conjugated nitrile ylides and diazoalkanes
Author: Cessford, Alastair G.
Awarding Body: University of Edinburgh
Current Institution: University of Edinburgh
Date of Award: 2002
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The cycloaddition reactions of a number of triene-conjugated nitrile ylides and diazoalkanes were studied. In all cases the a,b unsaturation was part of a benzene or thiophene ring and the g,d;e,ζ double bonds were olefinic. The nitrile ylides in which the trienyl system was in the trans configuration reacted exclusively via 1,1-cycloadditions to yield the corresponding 1-alkenyl-exo-cyclopropa[c]isoquinolines. These primary products were found to undergo intramolecular rearrangement reactions of three types to yield 4-alkenyl-1H-2-azepines, propenyl-bridged isoquinolines (or the thiophene analogue) or azabenzobabaralanes. It was found that the proportions of these products obtained were dictated by the substitution pattern of the precursor cyclopropa[c]isoquinoline, and, in each case, the observed reaction modes are rationalised in terms of substituent effects. Triene-conjugated diazoalkanes where the cis d substituent was hydrogen were found to yield exclusively the 4-alkenyl-1H-2,3-diazepines, presumably via a 1.7-electrocyclisatoin process. Where the cis d substituent was a phenyl ring and the ζ-substituent was an aryl group a 1,1-cycloaddition occurred, ultimately yielding the pyrrolophthalazines. Where either the d- or ζ-substituent of the diazoalkane was non-aromatic, carbene-derived products were formed via intermolecular reactions. Where the trienyl system was in the cis configuration at the g,d-bond the 1,1-cycloaddition process became less competitive and the major or exclusive products were the carbene-derived cyclopropa[a]naphthalenes. Greater proportions of the phthalazines were obtained where the ζ-substituent was aromatic. This effect is rationalised in terms of the stability of a proposed diradical intermediate for rearrangement of the primary cycloaddition product.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available