Mechanism Study Of 3d Transition Metal Ion Coordination-oriented Domino Reaction Of Benzo[d]azoles-2-methylamine Leading To Tetrasubstituted Pyrrole And Pyrazine

Achieving sustainable and controllable synthesis is one of the ultimate goals of chemical research.Starting from simple substrates and through continuous bond forming in a"one pot"to give the target molecules is a promising strategy to achieve this goal.The domino reaction can realize the continuous construction of multiple covalent bonds.The design and development of efficient domino reaction rely on the study of reaction mechanism,it is helpful to reveal the mechanism by tracking the reaction process.In the domino reaction,the continuous construction of C-C and C-X bonds catalyzed by transition metals have become a powerful tool to synthesize complex molecules.The coordination of metal ions with substrates promotes the formation of covalent bonds between substrates.Therefore,it is the key to develop new domino reaction modes by studying and developing the coordination modes between substrate and metal ions.Our research group has developed a series of domino reactions based on continuous coordination and activation between 3d transition metal ions and chelating substrates.The coordination can be regulated by changing the type and position of heteroatoms and heterocycles in the chelate-type substrate,so that different series sequences and corresponding complex cyclization products can be developed.To further explore the influence of heteroatoms on this kind of reaction.In this thesis,the type of heterocyclic ring was changed from benzimidazole ring to benzothiazole ring,benzo[d]thiazole-2-methylamine S1 and 1-methyl-1H-benzo[d]imidazole-2-methylamine L1was selected as substrates,and through its reactions with a series of 3d transition metal ions,two new domino sequences as well as three new heterocyclic compounds have been developed.Using electrospray ionization mass spectrometry（ESI-MS）and crystallography technology,the reaction process was tracked,and the possible mechanism was proposed,which laid the foundation for the design and development of domino reaction.This thesis includes the following four parts:Chapter 1 is the introduction,focusing on the development process and design strategy of series reaction,and combining with the preliminary work of the research group,proposed the topic of this paper.In chapter 2,the first tetraheteroaryl substituted pyrrole derivative HP（HP=2,2’,2’’,2’’’-（1H-pyrrole-2,3,4,5-tetrayl）tetrakis（benzo[d]thiazole））was produced by the reaction of chelating ligand benzo[d]thiazole-2-methylamine S1 with Mn²⁺under methanol solvothermal conditions.The dinuclear complex Mn2-P of pyrrole derivatives was obtained directly in the form of single crystal after the reaction.In contrast,four pyrazine derivatives S4（S4=2,3,5,6-tetra（benzo[d]thiazol-2-yl）pyrazine）substituted by benzo[d]thiazole groups were obtained by the control experiment without adding metal,and the corresponding pyrrole derivatives were obtained by adding alkynyl derivatives as intermediates,which suggested that in the formation of pyrrole derivatives,the coupling of two S1 via methylene group to produce the key intermediate alkynyl derivatives is promoted by Mn²⁺.The structures of these compounds were characterized by single crystal X-ray diffraction.Electrospray ionization mass spectrometry（ESI-MS）was used to track the reaction process,and intermediate fragments[I（Mn）-Cl]⁺(m/z _exp.=417.9874),[C+H]⁺(m/z _exp.=295.0357)and[D（Mn）+H]⁺(m/z _exp=692.9730)were detected,combined with free radical capture experiment and control experiment,a six-step domino reaction mechanism of HP synthesis involving coordination,amine self-condensation,free radical C-C coupling,deamination,[3+2]cycloaddition and aromatization was proposed.This work is the first time to realize the synthesis of pyrrole derivatives from a single methylene amine derivative through intermolecular reaction,which reflects the importance of metal ions for the development of diversity-oriented synthesis.In chapter 3,according to the discovery that the reactivity of S1 is dependent on metal ions,furthermore,the domino reaction of Fe²⁺,Co²⁺,Zn²⁺and S1 was explored.The fragments of substrate coordinated with metal center[I（Fe）-Cl]⁺(m/z _exp.=418.9843),[I（Co）-Cl]⁺(m/z _exp.=421.9832),[I（Zn）-Cl]⁺(m/z _exp.=426.9790)and a series of key intermediate fragments[C+H]⁺(m/z _exp.=295.0357),[II+H]⁺(m/z _exp.=310.0463),[D（Fe）+H]⁺(m/z _exp.=693.9716),[D（Co）+H]⁺(m/z _exp.=696.9718),[D（Zn）+H]⁺(m/z _exp.=701.9650)were detected by ESI-MS.The reaction time of different metal ions reacting with S1 to form intermediates and HP was systematically revealed by mass spectrometry tracking,The results showed that[HP+H]⁺was detected at 2 h,indicating that MnCl₂·4H₂O,FeCl₂·4H₂O,CoCl₂·6H₂O and ZnCl₂ all had good promotion efficiency.The photophysical properties of HP were studied,the excited state lifetime of HP in CH₂Cl₂(ca.1×10^-5 M)was1.09 ns,and the fluorescence quantum yield was 52.81%.In chapter 4,the reaction process and mechanism of synthesis of polycyclic substituted pyrazinederivativeS3L-Py（S3L-Py=2,2’,2’’-（6-（1-methyl-1H-benzo[d]imidazol-2-yl）pyrazine-2,3,5-triyl）tris（benzo[d]thiazole））by solvothermal domino reaction of Co²⁺and Fe²⁺with two methylene amine substrates L1（L1=（1-methyl-1H-benzo[d]imi-dazol-2-yl）methylamine）and S1 were studied.Binuclear 1,4-dihydropyrazine complexes Co2-S3L-HPy and Fe2-S3L-HPy were obtained directly in the form of single crystals after the reaction,and their structures were confirmed by single crystal X-ray diffraction technology,In which Co2-S3L-HPy was further characterized by X-ray photoelectron spectroscopy and infrared spectroscopy,which supported its1,4-dihydropyrazine skeleton.The reaction process of the synthesis of S3L-Py was tracked by ESI-MS,and four key intermediate fragments ⅰ（m/z=419.04）,ⅱ（m/z=417.02）,[ⅲ+H]⁺（m/z=307.10）and[1-CoCl₂+H]⁺were successfully detected.This work is the first time to obtain the complex of 1,4-dihydropyrazine.The luminescence properties of novel pyrazine derivatives S3L-Py and S4 were investigated.The fluorescence lifetimes of S3L-Py and S4 in CH₂Cl₂(ca.1×10^-5M)were 0.7972 ns and 1.0901 ns,respectively,and the corresponding fluorescence quantum yields were 18.57%and 2.82%.