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|Title:||Nitrenes in heterocyclic synthesis.|
|Presented at:||University of Leicester|
|Abstract:||Section I. Pyrolysis of l-acyl and l-aroylamino-8-azidonaphthalenes gives 9-amino-2-substituted naphth [l,2,-d]oxazoles and 2-substituted perimidines. This new synthesis of oxazoles involves nucleophilic attack by the amide oxygen at the naphthalene 2-position accompanying intramolecular acid catalysed decomposition of the azide. An acid catalysed rearrangement is observed in the conversion of m-azido- benzanilide to 5-amino-2-phenylbenzoxazole. Replacement of the amide H in the thermolysis reactions generally leads to 1,2-dihydrobenz [cd] indazole derivatives. Although l-azido-8-phthalimidonaphthalene only gave the corresponding perimidine. This formally involves nitrene insertion into a C=0 bond and stoichiometric loss of oxygen. Mechanisms for the formation of the oxazoles, indazoles and perimidines are discussed. Attempted synthesis of l,2-dihydrobenz [cd] indazole from dimethyl 1,2-dihydrobenz [cd] indazole dicarboxylate and from 1-amino- naphthalene shows that it exists in the more stable tautomeric forms with the aromatic indazole rather than naphthalene nucleus. Decomposition of l-amino-8-azidonaphthalene in the vapour phase results in direct insertion into an NH bond to give the indazoles. These indazoles can be reconverted into N,N-disubstituted dihydrobenz[cd] indazole derivatives but cannot be oxidised to benz [cd] indazole. Several other unsuccessful routes to this elusive heterocyclic system are discussed. Section II. Benz [cd] indole could not be isolated on oxidation of 1,2-dihydrobenz [cd] indole but products were isolated that could be rationalised by nucleophilic attack on benz [cd] indole. Photolysis of methyl 8-azido-1-naphthoate gave 2-methoxybenz [cd] indole but pyrolysis of this azide gave only the intermolecular dimer. Section III. Oxidation of the hydrazones of o-aminoacetophenone and o-aminobenzophenone gave 4-methyl and 4-phenylbenzo-l,2,3- triazine, the simplest derivatives yet prepared of this heterocyclic system. Oxidation of 1- and 2-amino-3-substituted indazoles also gave the benzotriazines. Attempts to make the parent benzo-l,2,3-triazine and to generate 1-azabenzocyclo- butadiene were unsuccessful. Mechanisms for the formation of the triazines are discussed. Section IV. "5-Nitreno-l,4-diphenyl-l,2,3-triazole" in equilibrium with a ring opened cyanide had been reported in the literature. All attempts to intercept this nitrene with established nitrene traps failed and it seems to us that the nitrene plays no part in the proposed equilibrium.|
|Rights:||Copyright © the author. All rights reserved.|
|Appears in Collections:||Theses, Dept. of Chemistry|
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