The Study Of Multicomponent Tandem Reactions Induced By Pyridinium Salts

Due to the aromatic character of the pyridine heterocycle, its basicity and the electron-attracting influence of the nitrogen atom, and the pyridine core is also a good leaving group, pyridinium salt is found having versatile chemical reactivities. Pyridinium cations can behave as electrophiles and 1, 3-dipoles to take part in condensation, Michael addition, 1, 3-dipolar addition, nuclear substitution and arrangement reactions. Pyridinium salts have vast applications to organic syntheses and especially in the synthesis of heterocycles. On the other hand, multicomponent reaction involving tandem process with at least three different simple substrates has emerged as a powerful synthetic strategy. The multicomponent tandem reactions or domino reactions offer significant advantages over conventional linear-type synthesis and step-by-step synthesis. This methodology allows molecular complexity and diversity to be created by the facile formation of several new covalent bonds in one-pot transformation with easier and less separation and purification. It's efficient and convenient, and is provided with atomic economy, and is quite closely approaching the concept of an ideal synthesis. So, it has become an important area of research in organic, medicinal and combinatorial chemistry. In this thesis we wish to report our study on the multicomponent reactions induced by pyridinium salts to prepare some cyclopropanes, benzene derivatives, nitrogen containing heterocycles and 2, 3-dihydrofurans with biological activity. A series of significant results and developments have been achieved and the main intriguing results are as follows:1. One-pot multicomponent reactions of pyridine, p-nitrobenzyl bromide, aromatic aldehyde and acetonitrile derivatives at room temperature were used to synthesize cyclopropane derivatives with triethylamine as catalyst. Under the similar reaction, the multicomponent reactions of aromatic aldehyde, pyridinium salts derived from N-(chloroacetyl)morpholine or N-(chloroacetyl)piperidine and malononitrile also yield cyclopropane derivatives. Totally fifty one new cyclopropanes were prepared and characterized by NMR, IR, LC-MS spectroscopy and single crystal structure of six cyclopropanes were confirmed by X-ray diffraction.2. The one-pot multicomponent reaction of aromatic aldehydes, malononitrile and 2-chloroacetic acid and pyridine in refluxing acetonitrile give the unreported five substituted benzenes in moderate yields. And the novel nitrogen containing heterocyclic compounds were produced in multicomponent reactions of malononitrile, aromatic aldehydes, chloroacetonitrile and excessive 3-picoline in refluxing acetonitrile. Twenty one new compounds were fully characterized by NMR, IR, LC-MS spectroscopy and confirmed by single-crystal X-ray diffraction of six compounds.3. Catalyzed by triethylamine the multicomponent reactions of aromatic aldehydes, activated bromomethyl compounds, Meldrum acid or 1, 3-dimethylbarbituric acid and pyridine derivatives in the room temperature produce the unreported zwitterionic compounds. When 1, 3-cyclohexandione, dimedone or 4-hydroxycoumarin was used in the reaction, new cyclohexyl fused 2, 3-dihydrofurans would be formed in high yields. Totally seventy six new compounds were characterized by NMR, IR, LC-MS spectroscopy and confirmed by single-crystal X-ray diffraction of three compounds.