Synthesis Of A Series Of Nitrogen-containing Cyclic Compounds

Nitrogen-containing heterocyclic compounds are a class of substances withphysiological and pharmacological activity. Among these compounds, the benzimidazoles, quinoxalines, indoles and their derivatives have been widely used in medicine, pesticides and dyes, etc. Therefore, the preparation of nitrogen-containing heterocyclic compounds is of great significances. The preparation of nitrogen-containing heterocyclic compounds via condensation reaction between amines with aryl/alkyl aldehydes is one of the main reaction types in organic synthesis. In this paper, several synthetic methods of pyrazines, benzimidazoles and indoles were selected and optimized. The target products were characterized by NMR to verify the structures.In this thesis,the progress of the synthesis methods of nitrogen-containing heterocyclic compounds, such as benzimidazoles, quinoxalines, indoles and their derivatives, are briefly introduced by reviewing the literature, and the advantages and short-comes of different methods are also summarized.The two preparing processes of the benzimidazole compounds,in which the o-phenylenediamine derivatives were condensed with acetylacetone or glacial acetic acid, respectively, were studied, and the reaction conditions were optimized. The synthesis of benzimidazoles was achieved by "one pot" method when the molar ratio of o-phenylenediamine to acetic acid equal to 1 to 2, the catalyst, polyphosphoric acid,is 10 times as much as the molar amount of the reactants, and the reaction time is 2?4 h generally. This reaction process is green and mild, and the starting materials are abundant.Lots of synthesis methods of the benzopyrazine derivatives have been reported in the literatures. The preparation of the benzopyrazine derivatives via the condensation between o-phenylenediamine and glyoxal is a suitable method for preparing benzopyrazine derivatives industrially. The overall reaction yield reached to 65 % when the molar ratio of o-phenylenediamine: acetic acid equaled to 1: 1.5 and the reaction time is generally 4 h. This method is environmentally friendly,time-saving and simple operation compared with the previous reported methods.In this thesis, a series of substituted-indole compounds were also prepared by the reaction of indole with substituted benzaldehydes. The target products were synthesized at room temperature with the overall yield above 69 % when the elemental iodine was used as catalyst and acetonitrile was used as solvent.