Research On Functionalization Reaction C-S(Se) And C-C Bonds Formation Of Indole Derivatives

Indole,the trivial name for benzo[b]pyrrole,is an important class of aromatic nitrogen-containing heterocyclic compounds,which is widely present in various pharmaceutical active molecules and natural products.As the core skeleton of medical drugs,agricultural chemicals,and functional materials,the importance of indole synthesis and its functionalization is self-evident.The functionalization of C-H bond as a general strategy in the field of organic synthesis provides a direct and efficient way to functionalize compounds.This paper researches the functionalization of indole derivatives by using indoles,ketones,aromatic alkynes and their derivatives and elemental sulfur(selenium)as raw materials.Hence,structurally-meaningful indole derivatives including thieno[2,3-b]indoles,selenopheno[2,3-b]indoles,benzoselenophenes bearing an indole moiety,benzo[a]carbazoles and 3,3'-diindolyl-2,2'-tetrasulfide heterocycles have been readily accessed.The detailed researches are described as follows:1.An efficient three-component thieno[2,3-b]indole formation method was developed under metal-free conditions.The cascade cyclization was enabled by acidpromoted annulation of indoles,ketones,and sulfur powder,which enabled the modular synthesis of 2-substituted and 3-substituted thieno[2,3-b]indoles with excellent regioselectivity and broad functional group tolerance.2.A facile metal-free entry to novel selenopheno[2,3-b]indole motif has been developed.The three-component assembly of indoles,aromatic ketones,and selenium powder are enabled by the IBr promoted highly selective double C-H selenylation/annulation.This method provides novel access to a diverse variety of selenopheno[2,3-b]indoles with good efficacy and broad functional group compatibility.3.An efficient three-component benzoselenophenes formation has been developed from substituted indoles,acetophenones,and selenium powder under metal-free conditions.The key 3-vinyl-indole intermediate was generated in situ through dehydrative condensation of aryl ketones and indoles under metal-free conditions.Benzoselenophene ring is synthesized by [4+1] cycloaddition reaction of the intermediate and selenium powder under the action of IBr.This simple method provides an efficient route for the preparation of a variety of new bis-heteroarenes bearing both indole and benzoselenophene moieties from readily available starting materials.4.A metal-free strategy for the synthesis of benzo[a]carbazoles from 2-arylindoles and aryl ketones(terminal alkynes)is developed.With IBr as promoter,chlorobenzene as solvent,these key intermediates could be selectively converted into the corresponding benzo[a]carbazoles via a direct cyclization process between two Csp2-H bonds.The reaction material is cheap and easy to obtain,and the substrate has good universality,which provides a convenient and efficient way for the construction of various substituted benzo[a]carbazole.5.Three-component "one-pot" synthesis of 3,3'-Diindolyl-2,2'-tetrasulfide using indole and elemental sulfur as the raw materials were studied.HI or the cheap and easily available Cu I as catalysts to promote tandem cyclization of indole and elemental sulfur,and elemental sulfur was used as "S4" source to construct octagonal ring with 3,3'-diindole.The reaction is simple to operate and the raw materials are readily available.