A study of the chemistry of some polycyclic mesoionic compounds
1983
The attempted synthesis of three different types of polycyclic mesoionic
systems containing the sydnone nucleus are reported. These systems
comprise the fused-aromatic ring mesoionic, the bismesoionic with direct
connection and indirect connection between the mesoionic nuclei.
The preparation of o-phenylene bissydnone has been achieved and the
characteristic 1,3-dipolar cycloaddition exploited using dimethylacetylene
dicarboxylate to prepare the corresponding bis~pyrazole. The di-bromo
derivative of the o-phenylene bissydnone has also been prepared and
characterised.
Several attempts to prepare a tetracyclic system by the coupling of
two mesoionic rings through an atom, such as sulphur, or a group, such
as carbonyl or thiocarbonyl have not been successful, but the coupling
of two sydnone rings together directly via the di-bromo derivative was
achieved. The resulting tetracyclic aromatic ring system represents both
bismesoionic (with direct and indirect connection) and fused-aromatic
ring systems.
The synthesis of both sydno[3,4-a]quinoxalin-4-one and -4-thione,
fused-aromatic ring compounds with the 5-niembered mesoionic sydnone
ring incorporated into a conjugated f used-ring heteroaromatic system,
have been achieved. Methyl, benzyl and amino derivatives of the sulphur
analogue of the quinoxaline derivatives have been prepared and
characterised. The success of the preparation of the quinoxaline derivatives
has been confirmed by comparison of the oxygen analogue with
an authentic sample of sydno [3,4-a]quinoxalin-4-one prepared by an
alternative route. Unsuccessful attempts to find further new routes to
the synthesis of sydno[3,4-a]quinoxalin-4-one are reported.
Several attempts to prepare bismesoionic systems containing different
mesoionic nuclei by building up mesoionic triazoles or thiadiazoles
on a preformed derivative of the sydnone or vice versa, are
discussed in the latter sections. Although the synthesis of this type
of bismesoionic system was not successful, potential precursors to these
systems were made, and a new method in the preparation of the mesoionic
l,2,4-triazolium-3-thiolate was developed.
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