Studies On C-H Activation And Cyclization Reactions Based On ?-Carbonyl Carbene Precursors

Compared with the traditional coupling reactions,the formation of new C-C bonds via C-H bond functionalization strategy is more step economical and significantly reduces the waste products.C-H bond activation has emerged as the holy grail in organic chemistry.Since it is unnecessary to introduce functional groups in advance,a new chemical bond is constructed by direct cleavage of C-H bond,which has peculiar advantages for the construction of new organic molecules.One of the most common strategies for C-H bond activation is based on the transition-metal and directing groups to achieve the cleavage of C-H bond and subsequent series of transformations.Diazo compounds are widely used in organic synthesis.In general,the preparation of diazonium compounds is safe and simple.Additionally,the ?-diazo carbonyl compound can form a Fischer metal carbene in the presence of a transition metal,and the reactive carbene intermediate can undergo the cyclopropanation reaction,the X-H insertion reaction(X = C,N,O,S,Si,etc.),new types of cross-coupling reactions,multi-component reactions,and others.In recent years,as an alternative strategy for C-H bond functionalization,more and more studies have been conducted on the functionalization of C-H bonds by diazonium compounds.Based on the our previous work on transition metal-catalyzed C-H activation reaction with diazo compounds.We first carried out the Rh(III)-catalyzed C-H activation reaction of 2-phenyl-1H-benzo[d]imidazole and 2-diazo-3-oxobutanoic and selective synthesis of ?-aryl ketone/ester.In this process,diazo compounds undergo selective fracture,which enables divergent C-H activation reactions of diazo compounds.Next,we selected 1-phenylpyrazolidine-3-ketone as the substrate for C-H activation reaction under the Rh(III)-catalyzed reaction system to achieve fluorine-containing pyrazine derivatives by using diazo compounds as coupling reagents.The reaction was studied by using cheap and readily available starting materials and Rh(III)as catalyst to successfully obtain novel products in a expedient way.Our group has also committed on other carbene systems,and sulfoxonium ylide has shown superior reactivity as carbene precursors.Thus,we have developed a radical cyclization reaction of sulfoxonium ylide,which could selectively produce two different five-membered cyclic compounds under the catalysis of copper salts or under the conditions of base,sulfur ylide and tert-butyl nitrite.In this process,the amount of sulfoxonium ylide and the metal catalysis play a crucial role for this divergent reaction.By using cheap and readily available starting materials as well as copper salt as catalyst,two distinct products are successfully obtained in a simple and effective approach.