Electron Deficient Enamine-based Cascade Reactions For The Synthesis Of Heterocycles

Small heterocycles consititute one type of the fundamental organic compounds,they play important role in many fields such as material science, pharmaceuticals.Therefore, the synthesis of heterocyles is a significant longstanding issue in the research of organic synthesis. This thesis mainly describes the work on the synthesis of heterocylic products via the cascade reactions based on electron deficient enamines.The contents consists of four major sections.Firstly, we investigated the multicomponent cascade reactions for the synthesis of1,4-dihydropyridines via the in situ generated enaminoester intermediates by the activation of secondary amine to alkynyl esters. The three-component synthetic methods using propiolates, aldehydes and primary amines have been established and a class of N-substituted 1,4-dihydropyridines were synthesized. Later on, by empoying ammonium acetate as the nitrogen source, we also successfully synthesized NH-containing 1,4-dihydropyridines.In the second sections, the three-component reactions of thioaceamide-based nitrogen source, adehydes and enaminones were studied. The produdcts of pyridine heterocycle were directly acquired. As extended scope, we employed electron deficient alkynes as alternative substrates of enaminones, and corresponding pyridines could be synthesized with good yields by simply adding catalytic amount of secondary amine. A new method for the multicomponent, one-step synthesis of pyridines was then developed.Subsequently, by also employing enaminones as main materials, we investigated and established the copper-catalyzed cascade reactons of enaminoes with ammonium as new approach for pyridine synthesis. Based on the different control experiments,we discovered that enaminone acted as the C4 building block to construct the pyridine ring via the oxidative cleavage of the C=C double bond. This method was applicable for the synthesis of both symmetrical and unsymmetrical pyridines.Finally, based on the oxidative activation of the enaminone C=C double bond, we established a method for the synthesis of benzothiazole containing 1,2-diketons via the cascade reactons of enaminones and o-aminothiophenols. The reactions proceeded in the presence of only molecular iodine. In addition, by modifiying the reaction conditions using CuI/oxidant, the selective synthesis of 2-aroyl benzothiazoles wasalso achieved.