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In this thesis, the author introduces two strategies used to
construct various types of N-heterocycles, based on the chemistry
of zirconacycles and 2,6-diazasemibullvalenes. In the first part,
the author presents the development of multi-component cyclization
of a zirconacyclobutene-silacyclobutene fused compound, nitriles
and unsaturated compounds. These reactions provide synthetically
useful methodology for various N-heterocycles such as 3-acyl
pyrrole, pyrrolo[3,2-d]pyridazine and dihydropyrroloazepine, which
are all difficult to synthesize by other means. The isolation and
characterization of the key three-fused-ring Zr/Si-containing
intermediates are also described in detail. These results show that
the zirconacyclobutene-silacyclobutene fused compound behaves as a
"chemical transformer" upon treatment with various substrates via
the "coordination-induced skeleton rearrangement" mechanism. In the
second part, the author demonstrates the synthesis and isolation of
a series of 2,6-diazasemibullvalenes (NSBVs) from the reaction of
1,4-dilithio-1,3-dienes and nitriles, highlighting the significant
progress made for the first time in this work: (1) determination of
X-ray crystal structure of a substituted 2,6-diazasemibullvalene;
(2) measurement of the activation barrier of its rapid
intramolecular aza-Cope rearrangement in solution; (3) exploration
of several reaction types of NSBV with diverse ring-expansion
products and "bowl-shape" or "cage-shape" N-containing polycyclic
skeletons; (4) demonstration of the localized structure as the
predominant form and the homoaromatic delocalized structure as a
minor component in the equilibrium using theoretical analysis.
Based on well-founded results, this work sheds new light on this
controversial topic.
In this thesis, the author introduces two strategies used to
construct various types of N-heterocycles, based on the chemistry
of zirconacycles and 2,6-diazasemibullvalenes. In the first part,
the author presents the development of multi-component cyclization
of a zirconacyclobutene-silacyclobutene fused compound, nitriles
and unsaturated compounds. These reactions provide synthetically
useful methodology for various N-heterocycles such as 3-acyl
pyrrole, pyrrolo[3,2-d]pyridazine and dihydropyrroloazepine, which
are all difficult to synthesize by other means. The isolation and
characterization of the key three-fused-ring Zr/Si-containing
intermediates are also described in detail. These results show that
the zirconacyclobutene-silacyclobutene fused compound behaves as a
"chemical transformer" upon treatment with various substrates via
the "coordination-induced skeleton rearrangement" mechanism. In the
second part, the author demonstrates the synthesis and isolation of
a series of 2,6-diazasemibullvalenes (NSBVs) from the reaction of
1,4-dilithio-1,3-dienes and nitriles, highlighting the significant
progress made for the first time in this work: (1) determination of
X-ray crystal structure of a substituted 2,6-diazasemibullvalene;
(2) measurement of the activation barrier of its rapid
intramolecular aza-Cope rearrangement in solution; (3) exploration
of several reaction types of NSBV with diverse ring-expansion
products and "bowl-shape" or "cage-shape" N-containing polycyclic
skeletons; (4) demonstration of the localized structure as the
predominant form and the homoaromatic delocalized structure as a
minor component in the equilibrium using theoretical analysis.
Based on well-founded results, this work sheds new light on this
controversial topic.
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