Synthesis And Evaluation Of Several Hydrotalcite-Supported Catalysts For Cyclization Of N-2-Alkynylaryl Sulfonamides

Indole and its derivatives are important nitrogen-containing heterocyclic compounds and have wide applications in many fields involving agriculture,medicine,and new materials.And therefore the development of new methods for constructing the indole ring system has been attracting interest in synthetic organic chemistry.The homogeneous metal-catalysized annulation of 2-alkynylanilides is one of the most powerful procedures used to generate indole compounds,while a few of drawbacks involving the catalysts such as high cost,unreusable,contamination of the final product and so on.And hence evaluation of green,efficient and reusable catalytic systems for synthesis of indoles is desirable.In this paper,hydrotalcite-supported catalysts were successfully prepared and screened for catalysis of ring-closure reaction of 2-alkynylaniline derivatives to indoles.It is divided into three sections.1.The traditional synthetic methods of indole and its derivatives were brifly reviewed.In particular,the recent research progress on the ring-closure reaction of 2-alkynylaniline derivatives to indoles was emphasized.2.Five hydrotalcite-supported catalysts,MgAl-LDH,ZnMgAl-LDH(5%Zn,w/w),FeMgAl-LDH(5%Fe,w/w),CuMgAl-LDH(5%Cu,w/w)and CuMgAl-LDH(2%Cu,w/w),were prepared by co-precipitation using a double drop technique.Their structures were confirmed by IR,XRD and TEM.Initial screening tests show that CuMgAl-LDH is the best catalyst for cyclization of 2-alkynylaniline derivatives to indoles among them.3.The optimized conditations for the cyclization of 2-alkynylaniline derivatives catalyzed by CuMgAl-LDH in ethanol were obtained and successfully applized to synthesize twenty one indole derivatives in quantitative yields in most cases.Both methanesulfonmides and 4-toluenesulfonamides of 2-alkynylanilines are suitable substrates for this new method.The structures of indole compounds synthesized were fully confirmed by IR,1H NMR and HR-MS.The crystal structures of nine typical indole molecules were also determined by X-ray diffraction techniques.In conclusion,an efficient and green method has been developed for synthesis of indoles by ring closure of N-2-alkynylaryl sulfonamides.