Palladium-Catalyzed Regiospecific Synthesis Of Indoles From Aroyloxycarbamates

The indole ring system is probably the most ubiquitous in heterocyclic compounds.Owing to the great structural diversity of biologically active indoles,it is not surprising that the indole ring system has become an important structural component in many active molecules and natural products.And they have a widely application in medicine,pesticide,perfume,dye,food,functional material fields.For over a hundred years,the synthesis and functionalization of indoles has been a major area of focus for synthetic organic chemists,and numerous methods for the preparation of indoles have been developed.Recently,the transition metal catalyzed indole synthesis and further functionalization have aroused much attention,especially the palladium and copper catalysts are of great significance.The experimental section includes two main parts and emphatically focused on the synthesis of indoles from aroyloxycarbamates using palladium catalyst.Firstly,we have offered a valuable strategy for the synthesis of 2-substituted indoles via Pd-catalyzed decarboxylation/cyclization of aroyloxycarbamates with terminal alkynes.The procedure involved decarboxylation in the presence of the palladium catalyst and cesium carbonate in toluene to provide the desired products with high yield.Next,we extended the scope of this newly developed methodology to prepare2,3-disubstituted indoles with the internal alkynes as the coupling partners.The palladium catalyst was efficient for the cascade decarboxylation/cyclization reaction to afford indoles with moderate yields.Employing general and easy available aroyloxycarbamates,this reaction generates indoles under mild conditions with high regioselectivity and excellent functional group compatibility.In this study,we obtained the optimum reaction conditions by studing the factors respectively which affect the reactions such as the catalyst,ligand,base,solvent and temperature.The structures of the compounds were confirmed by ¹H NMR,¹³C NMR,IR and LC-MS.We also conducted a preliminary exploration of the mechanism.