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|Title: ||Free radical cyclisation of imines|
|Authors: ||Young, Adrian R.|
|Issue Date: ||1996|
|Publisher: ||© Adrian Young|
The free radical cyclisation reaction onto an unsaturated bond is a well known
synthetic pathway, where a wide range of cyclic compounds can be produced form
acyclic starting materials. Up until recent years, free radical addition to multiple bonds
other than carbon-carbon had been little studied. Nowadays there is much information
available of radical addition to carbonyl, thiocarbonyl, nitrile and oxime ether (C=NOR)
functional groups. However there has been surprisingly little detailed study of similar
reactions involving imines (C=NR) or hydrazones (C=NNHR).
In the early phase of the research, different types of imine were synthesised and
subjected to the standard free radical cyclisation procedure (tributyl-tin hydride / AIBN,
added by syringe pump to refluxing solvent) to determination of the regiochemistry of
cyclisation onto imines and to assess the synthetic potential of the reaction. The results
of this investigative study show that a variety of five and six-membered ring compounds
can be synthesised in good yield. A similar study of hydrazones showed that fivemembered
rings can be formed under the same reaction conditions.
In the next phase, the aim was to extend the methodology to produce more
complex structures from acyclic starting materials. If a radical adds to the carbon atom
of an imine, a nitrogen-centred (aminyl) radical is generated which can undergo
subsequent addition to a suitably positioned double bond to yield a bicyclic amine. This
type of reaction is known as tandem or cascade cyclisation. By this method, compounds
could be synthesised which have similar structures to natural products. A range of
suitably designed imines wct.5. prepared and underwent cyclisation, producing many
different types of bicyclic amine in yields varying from moderate to good.
The Synthesis of Natural Products.
After the successful formation of key bicyclic structures, the third phase of the
research aimed at the synthesis of one or more of target natural products. The synthetic
strategy used in the tandem reactions outline above was. adapted for these purposes.
However the synthesis of the desired compounds could not be achieved in the time, but
progress towards their formation was achieved.|
|Description: ||A Doctoral Thesis. Submitted in partial fulfilment of the requirements for the award of Doctor of Philosophy of Loughborough University.|
|Appears in Collections:||PhD Theses (Chemistry)|
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