Study Of Functionalization Reactions Of Aza-aromatic Salts

Azacyclic compounds have important applications.They are widely distributed in natural products,pharmaceuticals,and fluorescent materials.More than 50% of the marketed small-molecule drugs contain azacycles.Functionalization of common aza-aromatics is one of the main tools for the development of new aza-ring classes.However,the functionalization of common aza-rings such as quinoline and benzothiazole is challenging because of their high thermal stability and kinetic inertness.Functionalization of aza-aromatic salts is an important synthetic approach for the construction of aza-ring skeletal compounds,a strategy that effectively activates aza-aromatic sites and allows the construction of complex aza-ring molecules.Accordingly,this thesis presents a series of potentially useful azacyclic compounds synthesized using the activation strategy of quinoline and benzothiazole for the efficient construction of azacyclic skeletons.The research content of this thesis is as follows.The first part of the work focuses on the de-aromatization and functionalization of quinoline salts using nano cobalt catalysis.De-aromatization coupling reactions of quinoline salts with tetrahydroquinolines are developed over nitrogen-doped carbon nano-cobalt catalysts.In this reaction,the C6 position of the tetrahydroquinoline is selectively coupled to the α-position of various quinoline salts for furnishing new 2-substituted N-alkyl-tetrahydroquinolines.A key strategy for initiating this reaction is the use of tetrahydroquinoline as an inert hydrogen source.The advantages of this hydrogen-transfer coupling reaction are excellent reusability,low cost,green reaction conditions,and excellent chemoselectivity.The second part of the work is to synthesize 2-methylbenzothiazole by ball milling method.This chapter describes a simple and practical method for the synthesis of2-methylenebenzothiazole from a benzothiazole salt coupled to 4-hydroxycoumarin.The reaction has a broad substrate scope and shows functional compatibility under mechanistic chemical conditions.Further,the reaction can be carried out without catalysts or solvents,thus being green and efficient.A series of luminescence performance tests revealed that the synthesized 2-methylenebenzothiazoles possess typical aggregation-induced luminescence properties,thus having the potential to become fluorescent materials.The third part of the work is to synthesize thiazepine-fused pyrrole derivatives based on the ring-opening/rearrangement strategy of 2-methylbenzothiazole salts.A one-pot three-component synthesis of thiazinopyrrole thick-ring derivatives from2-methylbenzothiazole salts,aldehydes,and amines was performed.The advantages of this reaction are the non-requirement of a catalyst,wide substrate scope,and functional compatibility with ethanol,a green solvent,which opens up new avenues for the synthesis of structurally complex azacyclic compounds.