Abstract
The subject matter of this thesis is concerned with
investigations of the synthesis and reactivity of bridgehead -
fused 1,2,3 -triazole derivatives. In particular the synthetic
usefulness of the products derived by acid -promoted triazole
ring cleavage in such heterocyclic systems was investigated.
The description of the results obtained in these studies is
preceded by a survey of methods commonly employed for the con-
struction of bridgehead -fused 1,2,3 -triazoles and an outline
of the types of reactivity which these compounds can exhibit.
The reactivity of a series of 3- phenyl- 1,2,3 -triazolo-
[1,5-a]pyrimidines towards protic acids has been studied and it
has been shown that in the case of hydrochloric and hydrobromic
acid triazole ring scission proceeds smoothly to afford the
respective 2- halobenzylpyrimidine derivatives. Attempts to
effect this reaction with a variety of other protic acids was
largely unsuccessful. The ability of Lewis acids to catalyse
triazole ring scission of 3- phenyl -1,2,3- triazolo[1,5- a]pyrimidines
was also investigated and it was found that the latter reacted
with boron trifluoride -etherate to give triazole cleaved products.
The intermediate boron trifluoride -1,2,3- triazolo[1,5- a]pyrimidine
adduct in such reactions was successfully isolated but attempts
to induce triazole ring cleavage of the complex by heating with
a variety of alkali metal salts met with mixed success.
Attempts to synthesise 2- aminobenzylpyrimidines by the
reaction of 2- chlorobenzylpyrimidines with aminating reagents
were not successful. In contrast it was found that the synthetically
useful 2- aminobenzylpyrimidines could be prepared by the
reduction of the corresponding 2- azidobenzylpyrimidines.
Acid -catalysed decomposition of the latter compounds also provided
a general route to 2- benzoylpyrimidines and the chemistry of these
little studied ketones was investigated. However, attempts to
use 2- benzoylpyrimidines to prepare novel bicyclic heterocycles
failed. 2- Aminobenzylpyrimidines were readily acylated by a
variety of acid chlorides and the resulting amides reacted with
phosphoryl chloride in 1,2- dichloroethane to give imidazo[1,5 -a]-
pyrimidine derivatives. The scope of this two -step acylationcyclisation
procedure was investigated in detail and provides a
general route to the little studied imidazo[1,5- a]pyrimidine
nucleus.
1,2,3- Triazolo[1,5 -a]- 1,3,5 -triazine derivatives were
prepared and the reactivity of this virtually unknown ring system
towards acid -promoted triazole cleavage was investigated. In
many cases such scission proceeded smoothly and provided a new
route to 1,3,5 -triazine derivatives. Attempts to synthesise
imidazo[1,5- a]- 1,3,5 -triazines failed due to the instability of
the 2- azidobenzyl- 1,3,5 -triazines required as precursors of the
key intermediate 2- aminobenzyl- 1,3,5 -triazines.
