Studies On Oxidative Ring-opening Of 1h-pyrazol-5-amines With Pyrrole-2-carboxaldchydcs And Rh-catalyzed The Reactions Of 3-DiazoindoIin-2-imines With Benzamides

Nitrogen-containing heterocyclic compounds are widely present in natural products,pharmaceuticals,pesticides,functional materials,organic synthons and other important molecules.Therefore,the research on the synthesis and functional group transformation of nitrogen-containing heterocyclic compounds has attracted significant attention in the field of organic chemistry.In recent years,the azoalkene intermediate has been developed which has a wide range of applications in synthesis of N-containing heterocycles.In the thesis,we employed the 1H-pyrazol-5-amines as precursors and proposed a method to afford a new type of azoalkene-3-diazenylacrylonitrile derivatives by the strategy of the dehydrogenation of the primary amino group which could lead to the ring opening of pyrazole.Then we investigated the reaction of 3-diazenylacrylonitrile with pyrrole-2-carboxaldehyde and construct the pyrazolo-pyrrolo-pyrazine scaffolds in one pot.The mechanism of the reaction was further studied by control experiments and DFT calculations.Studies suggest that the ring-opening of 1H-pyrazol-5-amines in the presence of PhIO could generate 3-diazenylacrylonitrile derivatives.The substrate of pyrrole-2-carboxaldehyde could undergo deprotonation in the presence of base.Subsequently,nucleophilic addition of the deprotonated pyrrole-2-carboxaldehyde to the alkenyl carbon of 3-diazenylacrylonitrile could trigger domino cyclization followed by dehydration to afford the final 3H-pyrazolo[3,4-e]pyrrolo[1,2-a]pyrazine derivatives.The advantages of this method are simple to handle and high atom-economy.In addition,this reaction could tolerate a broad range of substrates and proceed under transition-metal-free conditions.Indole and its derivatives are very important in nitrogen-containing heterocyclic compounds.3-Diazoindolin-2-imines have attracted the attention of chemists due to their ability to undergo diverse reactions which could construct a variety of indole derivatives easily and efficiently.We investigated the Rh(?)-catalyzed reaction of 3-diazoindolin-2-imines with benzamides and the 3-aryl functionalized indole derivatives are formed which shows high chemoselectivity and regioselectivity.The preliminary mechanism of the reaction was studied by DFT calculations,which suggests that the reaction is more likely to proceed via the ?-imino rhodium carbene intermediate followed by the insertion of the sp2 C-H bond.This method provides a new way for the synthesis of indole derivatives.