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Synthesis and transformations of B-nitroacetamides: Nef reaction and radical cyclisations

Gascoigne, ESJ; (2016) Synthesis and transformations of B-nitroacetamides: Nef reaction and radical cyclisations. Doctoral thesis , UCL (University College London). Green open access

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Abstract

This thesis details the investigations into the synthesis and further applications of β- nitroacetamides. The introductory chapter describes the initial discovery and development of the nitro-Mannich reaction, and its extension to the diastereo- and enantioselective formation of β-nitroamines and their derivatives. The use of the nitro functional group as a synthetic handle for the transformation of β-nitroamines and their derivatives is then described, with particular emphasis on reduction, Nef reaction and radical removal of the nitro group. The results and discussion section focusses on the formation of β-nitroacetamides via the deprotonative or conjugate addition nitro-Mannich reaction, and the subjection of these products to the Nef reaction, and towards radical denitration and in situ carbon-carbon bond formation. A wide variety of Nef reactions are described: base/acid hydrolysis, base/oxidation and reductive methods. Nef reactions using base were found to be incompatible with β-nitroacetamides due to an elimination reaction, however a reductive Nef reaction using CrCl2 effected the partial reduction of the nitro group to an oxime. Further attempts to reduce the oxime to the corresponding carbonyl functional group were unsuccessful. Nef reaction of β-nitroamines were also unsuccessful, mainly resulting in decomposition. Initial radical investigations found that a significant excess of tributyltin hydride was necessary for adequate conversion to the denitrated product. It was found that reaction in toluene can lead to the decomposition of β-nitroacetamides. A range of novel β- nitroacetamides with an intramolecular alkenyl- or alkynyl tether were synthesized. Cyclisations of the β-nitroacetamides were successful in most cases, undergoing 5-exotrig cyclisation to give the desired cyclopentyl or indanyl structures. Diastereoselectivity was low, with 2 or 3 of 4 possible isomers observed in many cases. Radical 1,4- translocation of a phenyl group was observed in several cases. Intermolecular radical addition to acrylonitrile was also achieved in good yield in the case of a more activated (benzylic) β-nitroacetamide.

Type: Thesis (Doctoral)
Title: Synthesis and transformations of B-nitroacetamides: Nef reaction and radical cyclisations
Event: UCL
Open access status: An open access version is available from UCL Discovery
Language: English
Keywords: Radical, Nef reaction, Radical Cyclisation, Radical Cyclization, Nitro-Mannich, Aza-Henry, Indanes, Cyclopentane rings, Nitro, nitroacetamide
UCL classification: UCL
UCL > Provost and Vice Provost Offices
UCL > Provost and Vice Provost Offices > UCL BEAMS
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences > Dept of Chemistry
URI: https://discovery.ucl.ac.uk/id/eprint/1515923
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