Tese de dout., Química, Faculdade de Ciências e Tecnologia, Universidade do Algarve, 2008In the course of this investigation, structural effects on the reactivity of a series
of heterocyclic compounds, in particular tetrazole and benzisothiazole derivatives,
submitted to different chemical environments, were explored.
The photochemistry of several representative tetrazoles was considered in
solution and for the compounds trapped in a rigid matrix of solidified argon at
cryogenic temperatures. UV-excitation resulted in photofragmentation of tetrazoles with
a wide range of exit channels. Important mechanistic questions concerning the
photodecomposition of allyl-tetrazolyl derivatives in different solvents were answered,
and new synthetic methodologies for the preparation of heterocyclic compounds, such
as pyrimidinones or oxazines, from allyl-tetrazoles, were developed.
For the matrix-isolated compounds, since the obtained fragments in general stay
in the matrix cage where they are formed, no subsequent cross-reactions involving
species resulting from photolysis of different reactant molecules can occur. This fact
introduced a useful simplification for the interpretation of the reaction mechanisms. FTIR
spectroscopy provided experimental frequencies and intensities of characteristic
absorptions of the matrix-isolated chemical species, both for reagents and
photoproducts. The analysis of experimental data was assisted by their direct
comparison with the vibrational spectra theoretically calculated for the single molecule
in vacuum. Spectroscopic characterization of a number of relatively unusual or highly
reactive molecules, formed from photolysis of matrix-isolated tetrazoles, is presented
for the first time.
Novel tetrazolyl and benzisothiazolyl naphthylmethylic ethers were synthesized
and the development of experimental conditions for their palladium-catalysed
hydrogenolysis, using a hydrogen donor or molecular hydrogen, was carried out
successfully. Structural effects on the reactivity of the heteroaromatic ethers were
investigated. Furthermore, new benzisothiazole-tetrazolyl derivatives differing on the
spacer-group used for linkage of the two heterocyclic systems were designed, produced
and tested as multidentate ligands in coordination reactions with transition-metal
complexes
