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Title: Gas-phase pyrolysis of amino- and amidomethylidene Meldrum's acid derivatives
Author: Withell, Kirsti
Awarding Body: University of Edinburgh
Current Institution: University of Edinburgh
Date of Award: 1998
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A range of new amino- and amidomethylidene Meldrum's acid derivatives have been prepared and subjected to flash vacuum pyrolysis. The N-substituents were chosen as potential groups for the expected pyrolysis products, pyrrol-3(2H)-ones. The initial use of silanes, hydrazines and benzylamines was not successful; silylamines were quantitatively deprotected on reaction with 5-methoxymethylidene Meldrum's acid (MMMA), hydrazine derivatives were successfully prepared but pyrolyses failed to produce protected pyrrolones and, although N-benzyl protected pyrrolones could be prepared, deprotection by hydrogenolysis did not take place at pressures up to 3 atm. A range of amidomethylidene Meldrum's acid derivatives were prepared by two complimentary routes; firstly, primary amides were reacted with MMMA to produce the desired compounds and secondly, aminomethylidene Meldrum's acid was directly acylated using acid chlorides. The second route proved to be the more efficient in terms of reaction times and yields. The formamidomethylidene derivative was studied in detail by NMR and X-ray crystallographic techniques and was shown to exist as two rotamers in both solution and solid states. All of the derivatives were successfully pyrolysed to give a general route to the parent 6H-1,3-oxazin-6-one and its 2-substituted derivatives (62-80%), many of which were previously unknown. Secondary cyclic amides also successfully gave amidomethylidene derivatives on reaction with MMMA. Pyrolysis of derivatives formed from 5-membered ring amides produced new bi- and tricyclic systems including 7a-methyl-1H-pyrrolizine-3,7(2H,7aH)-dione. The chemistry of this system was studied in detail, and proved to be unusual in comparison with simple pyrrolones. The compound was relatively unreactive towards electrophiles, although substitution did take place at the expected position. Conversely, it showed high reactivity towards nucleophiles though the mode of reaction depended on the nature of the nucleophile. Addition of thiophenol was shown to be completely diastereoselective by NMR studies and X-ray crystallography. Photolysis of the dione produced an unsymmetrical dimer whose structure was determined by extensive NMR studies. Methanolysis of the dione produced an N-unsubstituted pyrrolone, of which there are relatively few examples, and the chemistry of this compound was also investigated. Pyrolyses of derivatives produced from 6-membered ring amides were inconsistent, and produced a variety of unexpected products.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available