Studies On The Gold-Catalyzed Tandem Reactions For The Construction Of Heterocycles

In this thesis, the strategy of gold-catalyzed tandem reactions was discussed on the basis of literature review. In light of the extraordinary capacity of gold catalyst in the construction of chemical bonds and the efficiency of tandem reactions in building up complex molecules, this thesis mainly focuses on the development of gold-catalyzed tandem reactions for the construction of heterocyclic compounds. Under the gold catalysis, five series of oxygen (or nitrogen)-containing heterocycles having potentially biological activities were synthesized with high efficiency from simple and easily available starting materials. These heterocyles include3,4-dihydrocoumarins,4H-chromenes,3-carbonylated benzofurans,1,5-benzodiazepines, and4-fluorinated pyrazoles. Thus, this dissertation includes the following six parts:(1) Firstly, the development and the characteristic advamtages of gold catalyst were summarized. Some representive examples on the construction of heterocyclic componds via gold-catalyzed tandem reactions were reviewed, including single Au(I), single Au(III), and Au(I)/Au(III) redox catalytic systems. On the basis of abovementioned background, the main ideas for designing of this thesis are discussed.(2) Secondly, it has been found that temperature-controlled [1,3]-or [3,3]-sigmatropic rearrangement could be selectively achieved in the AuCl3/3AgOTf-catalyzed tandem rearrangement/cyclization of (E)-2-(aryloxymethyl)alk-2-enoates to afford diverse substituted patterns of3,4-dihydrocoumarin derivatives in moderate to good yields with excellent regioselectivity.(3) Thirdly, an efficient and highly selective approach for the synthesis of functionalized4H-chromenes has been developed via AuCl3/3AgOTf-catalyzed condensation/annulation tandem reaction of ketones with phenols for the first time. Up to99%isolated yield of4H-chromenes could be achieved.(4) Next, a highly regioselective protocol for the synthesis of3-carbonylated benzofuran derivatives has been developed involving a unique AuCl3/3AgSbF6-catalyzed tandem condensation/rearrangement/cyclization reaction of O-arylhydroxylamines with1,3-dicarbonyl compounds.(5) Furthermore, a novel and efficient protocol for the synthesis of1,5-benzodiazepines has been developed via (2-biphenyl)Cy2PAuNTf2- catalyzed amination/cyclization reaction of o-phenylenediamines with alkynes in moderate to excellent yields. The method represents the first example of an alkyne-based synthesis of1,5-benzodiazepines with100%atom-ecomomy.(6) Finally, in light of ubiquitous alkyne in organic synthesis, a mild and efficient protocol for the preparation of4-fluorinated pyrazoles based on gold-catalyzed tandem aminofluorination of alkynes in the presence of Selectfluor has been developed for the first time. The present method has advantages of mild reaction conditions, high yields, broad substrate scope, and a simple one-pot procedure.