Rh Catalyzed Intramolecular Annulation Of 1-Sulfonyl 1,2,3-Triazoles For Synthesis Of Pyranoindole Derivatives

Pyranoindole,famous for its interesting biological activities,is an important structural motif in many natural compounds.For the particularity of the skeleton structure,some of pyranoindole derivatives have pharmacological activity,so it is widely used in biomedical and agricultural fields.In a word,the scientists from the world are all concerned about to develop an efficient method to the synthesis pyranoindole derivatives.The methods of synthesizing pyranoindole compounds that have been reported are very limited,and most of them are using Oxa-Pictet-Spengler method,namely creating an acid environment to form the oxonium salt,and then nucleophilic attacted by indole to take place cycloaddition to form pyranoindole.However,there's a big defect in this method,that is when the desired products are unstable in the acidity,they will decompose or transfer to some other byproducts,somehow,this is a big narrows to the scope of derivatives.Until 2015,Gregorio Asensio's group using gold catalyst to synthesis pyranoindole without acid in reacting system,it means they have solved several problems fundamentally.Now we report a novel and efficient method to synthesize high stereoselectivity pyranoindole compounds,which utilizing Rh(II)-catalyzed intramolecular annulation of 1-sulfonyl 1,2,3-triazoles in neutral environment.Firstly we screening an optimized reacting conditions,and then we explore the substract scope as well as the functional group compatibility of our methodology.Testing whether electronic nature of the substituents at the indole ring and protecting group can influence the yield of the reactions significantly.In addition,we utilizing this mechanism to synthesis oxepinoindole smoothly and finding that the pyranoindole derivatives could be synthesized in "one-pot" starting from alkynes via Cu-Rh sequential catalysis.The model product was unambiguously confirmed by single crystal X-ray diffraction analysis.And a series of triazole derivatives and pyranoindole derivatives were characterized by 1H NMR,13C NMR,IR spectrum and ESI-MS.Based on our experimental findings and some relevant reports,the possible reaction mechanism were proposed.