Tandem Cyclization Reaction Of Diene Radicals And The Conversion Of Xanthenes To Thioketones

Due to its unique structural characteristics and wide applications,olefins are widely used as raw materials in various reactions in synthetic chemistry to construct high value-added products.Radical reactions,which are characterized with high atom economy,clean and efficient reaction process,and environmental friendly,are used as irreplaceable strategies in the construction of C-C and C-hetero bonds.Especially in recent years,radical initiated tandem cyclization of olefins has been extensively developed.However,there are still many challenges needed to be solved by chemists.Thienone is a universal building block in organic synthesis and is ubiquitous in natural products and pharmaceutical molecules.It can also serve as the directing group（DG）to promote the transition-metal catalyzed functionalization of o-C-H bonds.In addition,they also have attractive photochemical properties.This work in this thesis is divided into two types:1.synthesis of nitrogen-containing heterocyclic compounds through tandem cyclization reactions induced by various free radicals with dienes as raw materials.2.Direct synthesis of thiophenes from xanthenes.The main research content is the following three parts:（1）Iron-catalyzed cascade cyclization of diene and ester radicals.An iron-catalyzed radical cascade cyclization of dienes initiated by alkoxycarbonyl radical has been developed in the presence of（NH₄）₂S₂O₈,leading to a series of fused nitrogen heterocyclic compounds under relative mild reaction conditions.The reaction is triggered by the addition of alkyoxycarbonyl radical derived from the cleavage of alkoxyformyl hydrazide.Afterward,the formed nucleophilic radical preferred the addition to the electron-neutral vinyl rather than the electron-deficient vinyl,followed by cascade 6-endo cyclization and further radical cyclization.（2）Iodine-promoted synthesis of thienones from xanthenes.The iodine-promoted direct conversion of xanthenes to thioketones using potassium ethyl xanthate as the sulfur source was developed.The reaction procedure featured with easy operation and good functional group compatibility,which represents as a reliable method to direct synthesis of thioketones.（3）Silver/Zinc-promoted synthesis phosphonylated and silylated fused nitrogen heterocycles from dienesOn the basis of our first work,we studied the phosphonylation and silanization reactions of dienes with phosphine oxide and triethylsilane under the catalysis of silver or zinc for the synthesis of phosphonylated and silylated fused nitrogen heterocycles.Cascade radical addition and cyalization were involved in these reactions,which opens up a new avenue for the construction of phosphonylated and silylated fused nitrogen heterocycles.These work needs to be further investigated.