Iodine-Catalyzed Indole C-H Bond Activation Reaction

Indole and its derivatives are a kind of very important nitrogen-containing heterocyclic compounds,which have been widely used in the fields of pharmaceutical molecules,pesticides and materials chemistry.Therefore,it is a very important subject to study highly selective synthetic methods to obtain structurally diverse indole molecules;Secondly,the indole molecule has large conjugation,so it has very important applications in the field of optoelectronic materials.In this paper,the indole C-H bond activation reaction catalyzed by iodine is mainly studied.The main contents are as follows:In the first part,the iodine-catalyzed 2-sulfonylation reaction of direct C-H bond between indole and arylsulfonyl hydrazide was investigated.The optimal conditions were:indole（0.5 mmol）and arylsulfonyl hydrazide（1 mmol）,potassium iodide（1 equiv.）,hydrogen peroxide（1 mL）,and react at room temperature for 5 min.This experimental method has a wide range of substrate applicability and tolerance of functional groups.Different substituted indole can react with arylsulfonyl hydrazide.It is important to use 30%H₂O₂ solution as oxidant and solvent in 5 minutes.Good yields can be obtained.The system has short reaction time,green oxidant and solvent,cheap iodine source,avoids the use of acid,and has a wide range of substrate applicability.The mechanism study showed that 2,3-diiodoindolinoline may be the main sulfonylation intermediate in this transformation.In the second part,3-arylthioindole and 2-arylthiopyrrole were obtained by direct thioetherification of N-heteroarene with ethyl arylsulfinate catalyzed by NH₄I/1,10-phenanthroline.The optimal conditions are:indole（0.3 mmol）,ethyl benzenesulfinate（0.4 mmol）,NH₄I（20 mol%）,1,10-phenanthroline（10 mol%）,HOAc（0.5 mL）1,4-Dioxane（2 mL）was reacted at a temperature of 100℃ for 6 h.This method has a wide range of substrate applicability and functional group tolerance.In the presence of a slight excess of arylsulfinate,the direct thioetherification of N-heteroaromatic hydrocarbons（indole and pyrrole）proceeds smoothly with a high yield.Between43-99%,and this method can also be used for the synthesis of gram scale reactions.Compared to traditional methods,this reaction does not require metal participation and uses readily available ethyl arylsulfinate as a sulfur reagent.Finally,through a mechanism study,the reaction was initiated by protonating ethyl arylsulfinate under acidic conditions and adding an iodide anion.In summary,this paper is based on the iodine catalyzed C-H bond activation reaction of indole,and through a direct C-H bond activation reaction with arylsulfonyl hydrazide and arylsulfinate,a series of 2-sulfonylations have been synthesized with high selectivity derivatives of indole and 3-arylthioindole have perfected and supplemented the functionalization of C2 and C3 positions of indole.