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|Title:||N-nitrenes and electrocyclic reactions in nitrogen heterocycles.|
|Authors:||Horwell, D. C.|
|Presented at:||University of Leicester|
|Abstract:||This thesis is divided into 3 parts. The first describes the preparation of several heterocyclic N-amino compounds and the generation from these of singlet amino-nitrene, by lead tetraacetate oxidation. These nitrenes, which undergo several different electrocyclic reactions, are of two broad types. The first, formed from N-aminoquinazolones, and an N-aminoquinolone, pyrimidone, pyridone and benzimidazole undergo intermolecular reactions, such as tetrazene formation and deamination. With a wide range of electrophilic and nucleophilic olefins they give aziridines stereospecifically, and with dimethyl sulphoxide they give the sulphoximines in high yield. The second type of amino-nitrene, formed from N-aminophthalazones and indazoles, mainly undergo intramolecular reactions involving extrusion of nitrogen. The phthalazones gave highly reactive 1-oxoisoindoles or azacyclopentadienones. The indazoles gave a complex pattern of products which could be rationalized by the intermediacy of a new anti-aromatic system, 2,3 benzoazete, or 1-azabenzocyclobutadiene. Differences between the two types of N-amino compounds are explained simply in terms of their structure. In the second part, the synthesis of indano[1,2-b] aziridine and its N-substituted derivatives is described, and their subsequent ring expansion to isoquinoline, in an aza-analogue of the cyclopropyl to allyl cation rearrangement. This is discussed in terms of orbital symmetry control. Rearrangement occurs in low yield with the N-chloro compound and in high yield by lead tetraacetate oxidation. In the third part, a PMR investigation of slow nitrogen inversion in aziridines, prepared from five N-amino compounds by their oxidation in the presence of acrylate and methacrylate esters, revealed an unexpected change in invertomer ratio as the size of the ester alkyl group was increased. This trend is rationalized in terms of an attractive interaction between the ester carbonyl group and the N-heterocyclic substituent. The use of this technique to compare group sizes provides a valuable supplement to cyclohexane conformational analysis.|
|Rights:||Copyright © the author. All rights reserved.|
|Appears in Collections:||Theses, Dept. of Chemistry|
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