|dc.description.abstract||The effect of scale on the conversion to products in flash vacuum pyrolysis
experiments was studied using four model reactions. Overall, conversion was
dependent on rection scale up to 0.5 g, but above 0.5 g, the effect was minimal and
within experimental error. This effect was shown to be due to variations in contact
time of the molecules in the furnace tube. Altering the furnace tube diameter had the
effect of increasing the conversion to product.
The pyrolysis of ortho-anilinomethylene Meldrum’s acid derivatives was
investigated. Typically the 8-substituted quinolin-4-one was obtained as the major
product, with a few exceptions. Certain substituents (such as nitro) were found to
react with the ketene produced in the reaction to give alternative products, while
others (such as chloro- and N-unsubstituted amides) gave the 3-substituted quinolin-4-
ones via ipso-cyclisation and migration of the substituent.
The regioselectivity of the pyrolysis of meta-anilinomethylene Meldrum’s acid
derivatives, to give 5- and 7-substituted quinolin-4-ones, was studied. In general a 3:1
– 4:1 ratio of regioisomers was obtained, in favour of the 7-substituted quinolin-4-one.
Substituents capable of hydrogen bonding, such as hydroxy-, were shown to give the
5-substituted quinolin-4-one exclusively and DFT calculations were employed to
show that, in these examples, the 5-substituted product was favoured energetically.
The pyrolysis of the methylene Meldrum’s acid derivative of 3-aminophenol
gave 8-hydroxyquinolizinone as the sole product at low temperatures, with 5-
hydroxyquinolinone as the major product formed at higher temperatures. The
mechanism involves a regioselective electrocyclisation, followed by a hydrogen
transfer and generation of a new ketene. Cyclisation of this ketene gives the
quinolizinone. The scope of this reaction was explored, with a number of derivatives
synthesised, and substitution on the aminophenol and the ketene generator was
tolerated. The reactivity of the quinolizinones was also explored. The hydroxygroup
was found to be phenol-like and underwent similar reactions, such as
alkylations and acetylations. The compound was found to be highly reactive towards
electrophiles, reacting in the 1- and 3- positions of the ring system, often in both
The pyrolysis of the aminomethylene Meldrum’s acid derivatives of certain
pyridazinones was shown to give pyridopyrazidinediones. In some examples, a
second product based on a pyrrolopyridazine ring system was observed and DFT
calculations show that the mechanism involves probably an electrocyclisation,
followed by a decarboxylation reaction.
Pyrolysis of amino acid ester derivatives of methylene Meldrum’s acid were
shown to give N-unsubstituted 3-hydroxypyrroles and 1H-pyrrol-3(2H)-ones.
Different amino acids were tolerated in the reaction, as were different electronwithdrawing
groups in place of the amino acid ester. DFT calculations were
employed to explore the mechanism of the reaction. 3-Hydroxypyrrole was also
synthesised from the pyrolysis of Meldrum’s acid derivative of glycine tert-butyl ester,
and the reactivity of the compound explored for the first time. The compound was
found to be reactive towards electrophiles, such as diazonium salts, and could be O-acetylated
under appropriate conditions.||en