Single Electron/Hydrogen Transfer-mediated Construcion And Structural Modification Of Six-membered N-heterocycles

N-heterocyclic compounds,especially six-membered N-heterocyclic compounds,play an important role in biomedical and functional materials,which are a class of indispensable substances related to the people's livelihood and sustainable development.Meanwhile,alcohols and cyclic amines are organic hydrogen-rich compounds that are widely found in nature.Highly efficient utilization of these inexpensive and abundant organic hydrogen-rich resources?alcohols and cyclic amines?and converting them into high-value products that meet human needs is a research topic that meets the requirements of sustainable development.Catalytic dehydrogenation and hydrogen transfer reactions are basic and important processes in organic synthesis and catalysis,and they are also a kind of organic synthesis reaction strategy with high atomic economy.Dehydrogenation and hydrogen transfer processes are characterized by atomic economy and greenness,and can quickly build chemical bonds,thereby achieving the functionalization of organic compounds and the construction of important skeletons/fragments.Under the above context,the research of this thesis mainly contains“single electron/hydrogen transfer-mediated construcion and structural modification of six-membered N-heterocycles”.The details are as follows:Capter 2:By employing reusable nanocobalt oxides as the catalysts,a site-specific oxidative C-H chalcogenation of?hetero?aryl-fused cyclic amines with various thiols and diselenides is presented for the first time.The reaction proceeds selectively at the sites of the?hetero?aryl rings para to the N-atom,and enables access to a wide array of chalcogenyl N-heteroarenes.The merits of the transformation involve high step-and atom-efficiency,excellent substrate and functional compatibility,operational simplicity,and the use of a naturally abundant Co/O₂ system.The present work offered a fundamental basis for the selective synthesis of functional N-heteroarenes from readily available feedstocks.Capter 3:Herein,by the employment of alcohol resources as green hydrogen source/reductant,the synthesis of N-heteroarene-fused cyclic amine derivatives by hydrogen transfer coupling reaction is reported for the first time.Firstly,unprecedented2-aminotetrahydronaphthyridine-based unsymmetrical P^N^P ligands and the related pincer manganese complexes were preparated.Their catalytic performance toward a new reductive cross-coupling of indoles/pyrroles with non-activated N-heteroarenes was evaluated.Using Mn-II as a most suitable catalyst and isopropanol as hydrogen sources,the transformation allows direct access to indole/pyrrole core-linked N-heteroarene-fused cyclic amines,a class of com-pounds with the potential for the discovery of functional molecules.The developed chemistry has established a unique system for the exploration of new catalytic reactions.Capter 4:To date,although tremendous advances have been made on N-heteroaryl C-H functionalization,there remain significant unmet challenges in deconstruction of extensively applied but poorly reactive N-heteroaromatics to useful frameworks.Here,by a strategy merging hydrogen transfer and selective coupling,an unprecedented ruthenium-catalyzed deconstruction of N-heteroaromatics to functionalized arylamines with 2-aminoaryl methanols was presented.The reaction is achieved via sequential functionalization of the?and?-sites of the initially formed N-heteroarenium salts followed by a C-N cleavage,proceeding with the striking features of broad substrate scope,excellent functional groups tolerance,high chemo-selectivity and atom-efficiency,and applicable for streamline synthesis of some potentially biomedical molecules that are difficult to prepare with the conventional approaches.The strategy employed will open new avenues for further development of valuable transformations of inert organic systems.Capter 5:The preparation of a series of cyclometalated iridium?III?complexes was reported.Among them,Ir-3 featuring a 2-?4-methoxyphenyl?-1,8-naphthyridyl ligand exhibits the best catalytic performance toward the hydrogen transfer-mediated annulation reaction of2-nitrobenzylic alcohols with readily available alcohols and gaseous ammonia.The catalytic transformation proceeds with good substrate and functional group compatibility,high step and atom-efficiency,no need for additional reductants,and liberation of H₂O as the sole byproduct,which endows a new platform for direct synthesis of valuable quinazolines.Mechanistic investigations suggest that the non-coordinated N-atom in the ligand serves as a side arm to significantly promote the condensation process by hydrogen bonding.The work paves the avenues for further development of hydrogen transfer-mediated coupling reactions by design of catalysts bearing N-side arm ligands.In conclusion,through the single electron/hydrogen transfer-mediated bonding mode,the research of this thesis provide new efficient and green methods for the efficient construction and direct modification of N-heterocycles and enrich the connotation of organic synthesis methodology.