Study On Ru(?)-Catalyzed Regioselective [3+2] Spiroannulation Of 2H-imidazoles With 2-Alkynoates

Spirocyclic skeletons,as the core component of many drug molecules,functional materials and ligands,have been the focus of research in the field of organic chemistry.However,the traditional strategies for synthesizing spirocyclic compounds mainly construct ring-by-ring,which usually have the disadvantages of complicated steps,low yields and poor selectivity.Therefore,it is of great significance to develop convenient and efficient methods for the synthesis of spiro compounds.Recently,with the rapid development of the C-H activation,the directing group assisted [3+2] cyclization reaction catalyzed by transition metal has been widely explored,providing a straight forward route to access cyclic compounds.However,up to now,ketimine “C=N” with a withdrawing group has been focused as the directing group(such as sulfonylketimine,acylketimine,etc.),which limited the scope of the substrates and chemical modification of the products.On the other hand,2H-imidazoles are important motifs and widely present in many biologically active natural products as well as important intermediates in organic synthesis.In thesis,we disclose a novel protocol of ruthenium-catalyzed cyclization of2H-imidazole and 2-alkynoates to afford spiro[imidazole-4,1'-indene] and its derivatives(Scheme 1).In this reaction,the 2-alkynoate as C2 synthesizer exhibits extensive functional group modification.Obviously,this strategy features good reactivity,broad substrate scope,good functional group tolerance and high regioselectivity.What's more,the useful allyl group can be easily introduced to the products at the free NH position,which makes this reaction particularly attractive for further transformation.In addition,the reaction mechanism was proposed based on the results obtained and literatures(Scheme 2).