Novel Cascade Reactions Based On Electron Deficient Enamines For The Synthesis Of 1,2-Diketones And N-Heterocycles

Owing to their advantages of high efficiency, greenness and diversity in reaction models, cascade reactions have been widely used in the synthesis of medicines, natural products and materials etc, and ocuppy significant position in current research of organic synthesis. This thesis mainly presents our research results on the designation of novel cascade reactions for the synthesis of diketones, quinoxalines, 1,2,3-triazoles and 1,2-dihydropyridines by employing electron deficient enamines such as enaminones, enaminoesters and nitroenamine etc as key starting materials or intermediates.The contents consist of three major sections.In the first section, the reactions based on the enaminone C = C double bond were studied. Under ambient conditions, the visible-light catalyzed synthesis of vicinal diketones was accomplished via the C=C bond oxidation in ethyl lactate in the presence of Rose Bengal. On the basis of this transformation, the one-pot synthesis of quinoxalines was also achieved under identical photocatalytic conditions by employing o-phenylenediamines as reaction partners to capture the in situ generated vicinal diketone intermediates.In the second section, we investigated and established the selective three-component cascade reactions for the synthesis of 1,5- and 1,4-substituted 1,2,3-triazoles. Firstly, the synthesis of 1,5-substituted 1,2,3-triazoles was achieved via the reactions of enaminones, primary amines and tosylhydrazine via the catalysis of molecular iodine. The synthetic system were uniquely advantageous for the metaland azide-free conditions, high regioselectivity etc. Subsequently, instead of p-tosylhydrazine, tosyl azide was employed as nitrogen source. By means of prior FeCl3-catalyzed transamination between enaminoes and primary amines, the subsequent employment of a base and the tosyl azide enabled the selective synthesis of 1,4-substituted 1,2,3-triazoles.The reactions were performed at room temperature without requiring isolation of the intermediate. As extended explore, the synthesis employing electron deficient alknyes as alternative substrates of enaminones were investigated. In the presence of secondary amine, the electron deficient alkynes were activated to provide enaminoester intermediates, and the reactions of the intermediates with primary amines, tosylhydrazine/tosyl azide enabled respectively the three-component synthesis of 1,5-/1,4- substituted 1,2,3-triazoles,.In the third section, we designed and achieved the three-component reactions of enals, enaminones and 2-aminopyridines for the synthesis of 1,2-dihydropyridines. The synthetic system employed cheap acetic acid and phenyl sulfonic acid as catalysts, and showed high product yields and broad application scope. Control experiments suggested that enaminones might firstly react with enals via Henry-type reaction, and then incorporated 2-aminopyridines to form 1,2-dihydropyridines via cascade transformations.