Application Of Gold-complexes In Transfer Hydrogenation Reaction And β-Enamino Ketones (Esters) Interrelated Reaction

In this thesis, we have discovered that gold(Ⅰ) complex catalyzed reductive amination of aromatic aldehydes under transfer hydrogenation conditions. We also developed an efficient synthetic method for β-enaminones and β-enaminoesters catalyzed by gold(Ⅰ) under solvent-free conditions. We extended the application of β-enaminones and β-enaminoesters in synthesis of indolequione and polysubstituted pyrrole derivatives.The research work of this thesis includes:Part1. Direct reductive amination of aromatic aldehydes catalyzed by gold(Ⅰ) complex under transfer hydrogenation conditionsTransfer hydrogenation reaction is one of the most significant and synthetically useful methods in organic chemistry. In the past decades, there were few reports shown that supported gold nanoclusters are efficient heterogeneous catalysts for transfer hydrogenation. However, there was no one report the homogeneous gold catalyzed transfer hydrogen reaction. The direct reductive amination of aromatic aldehydes has been achieved with excellent isolated yields using readily accessible Ph3PAuCl/AgOTf catalyst along with ethyl Hantzsch ester as hydrogen source under mild reaction conditions. Aromatic amines could reacted with aromatic aldehydes and heteroaromatic aldehydes smoothly. When aliphatic ketones were used, such as butanone, cyclopentanone and cyclohexanone, good yields were obtained at higher reaction temperature. The catalytic mechanism for this reaction is probably through a proton-catalyzed hydride transfer process. The catalyst Ph3PAuOTf is partially hydrolyzed with traces of water, and provides the proton which can protonate the imine. The resulting iminium can then be reduced by the ethyl Hantzsch ester as the hydride source.Part2. Efficient synthetic method fo β-enaminones and β-enaminoesters catalyzed by gold(Ⅰ) under solvent-free conditions.β-Enaminones and β-enaminoesters are highly useful building blocks that play crucial roles in the synthesis of heterocycles and biologically active compounds. Arcadi reported gold (Ⅲ) derivatives could catalyze the condensation reaction of1,3-dicarbonyls and ammonia/amines, however, the kinds of amines were limited and low yiled was obtained when aromatic amines was used. An efficient method has been developed for synthesis of β-enaminones and β-enaminoesters via reaction of1,3-dicarbonyl compounds with various aliphatic and aromatic primary amines catalyzed by [(PPh3)AuCl]/AgOTf under solvent-free conditions. This methodology affords kinds of β-enaminones and β-enaminoesters derivatives in good to excellent yields. Moreover, the method has the advantage of easy manipulation and mild reaction conditions.Part3. Synthesis of indolequiones through bromoquinones and enamines with gold(Ⅰ) catalyst.We have developed an efficient method for synthesis of β-enaminones and β-enaminoesters. We start with2-bromonaphthalene-1,4-dione to synthesize bioactive molecules. The effecets of solvents, amount of base and diffferent gold catalysts were discussed, under the optimized conditions, a variety of β-enaminones and β-enaminoesters were screened to evaluate the scope of this reaction. From the results, we clearly see that the substituents of β-enaminones or β-enaminoesters were aromatic properties, the reaction took place very badly when it was aliphatic substituents, the reaction took place very well. In symmary, the application of gold in organic synthesis is further extended, which make it possible to achieve the heterocyclic compounds.Part4. Gold (I) catalyzed synthesis of polysubstituted pyrroles from β-enamino ketones or esters and (E)-1-nitro-2-phenylethylene.Densely substituted pyrroles are an important class of heterocyclic compounds with useful biological and physical properties. the classical methods for the synthesis of pyrroles is Knorr reaction, Hantzsch reaction, and Paal-Knorr condensation reaction. However, some of them usually present significant limitations, such as tedious workup, harsh nature of reaction conditions, low yields, long reaction times. Therefore, the continuous studies for the synthesis of pyrroles in terms of efficient, environmental benign, operational simplicity, economic viability, and high selectivity are still of great significance. we have successfully developed a novel, operationally simple, economical, and environmentally friendly reaction to synthesis functionalized pyrroles by employing β-enaminones (esters) and trans β-nitrostyrene. This method is quite general and it works well with a wide variety of β-enaminones (esters). The major advantage of this method is low catalyst loading (1%mol).