The Chemistry of Zirconacycles and 2,6-Diazasemibullvalenes

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.

Nominated by Peking University as an Excellent Doctoral Dissertation Describes the synthesis of synthetically useful N-heterocycles using Zr/Si-containing intermediate as a "chemical transformer", which are difficult to synthesize by other means Presents in detail the determination of X-ray crystal structure, the measurement of activation barrier of aza-Cope rearrangement, as well as the new reaction chemistry of 2,6-diazasemibullvalene (NSBV) Demonstrates for the first time the localized structure of NSBV as the predominant form and the homoaromatic delocalized structure as a minor component in the equilibrium via theoretical analysis Research work was highlighted by J. Am. Chem. Soc. Spotlight Includes supplementary material: sn.pub/extras

Inhalt
Introduction to Zirconacycle Chemistry.- Zirconocene-Mediated Cyclization of Bis(alkynyl)silanes and Nitriles: Synthesis of N-Heterocycles and Isolation, Characterization and Synthetic Application of Zr/Si-containing Reactive Intermediates.- Bulky-Nitrile Coordination Induced Skeleton Rearrangement of Zr/Si-containing Metallacycles and Selective Synthesis of 5-Azaindoles.- Introduction to Semibullvalenes and Azasemibullvalenes.- 2,6-Diazasemibullvalenes: Synthesis, Structure, Theoretical Analysis and Computational Chemistry.- 2,6-Diazasemibullvalenes: Reaction Chemistry and Synthetic Application.