Theoretical Study On Mechanism Of Phosphine Catalyzed Cycloadditions Of Enynes With Allenoate And Rearrangement Of Alkylidenecyclopropanes

Ring structure is one of the key structures in organic chemistry.It has attracted much attention in the fields of total synthesis of natural products and development of new drugs.In this paper,the density functional theory(DFT),polarized continuum model(PCM)and transition state theory(TST)in quantum chemistry are used to calculate and analyze each step of the reactions.After selecting a reasonable algorithm and basis set,the potential energy surface of the reaction was obtained through structural optimization and frequency analysis.Further detailed study of the reaction mechanism was carried out to provide theoretical basis for further experimental research.This work will be discussed in four parts.Chapter one: Research background.This chapter briefly introduces the recent development of organic small molecule catalysis,the important role of organic phosphine catalyst in organic synthesis,the knowledge of proton shift and proton transport assistant,and the research progress of phosphine catalyst catalysis synthesis of five-membered heterocyclic ring and other structures.Chapter two: Overview of theoretical basis.This chapter briefly introduces the development history of quantum chemistry,density functional theory,transition state theory,solvation effect model,Multiwfn analysis method and other related knowledge.Chapter three: Quantum chemistry methods was used to study the mechanism of phosphine-catalyzed [3 + 2] cycloadditions of trifluoromethyl enynes with allenoates.The detailed calculation and analysis for all paths of the reaction are involved.The surface electrostatic potential and weak interaction analysis for key intermediates and transition states are employed to explain the selection of the pathway,the origin diastereoselectivity and proton transfer.Chapte four: The density functional theory methods were employed to explore the mechanism of phosphine-catalyzed rearrangement of alkylidenecyclopropanes to generate polysubstituted furan and dienone.First,the ring-opening reaction of subalkylmethylcyclopropane was initiated with the participation of phosphonides,and then the five-membered ring was closed by the path A to the ring-opening site(while the catalyst was removed),and then the product of trisubstituted furan was obtained by isomerization.Two-step hydrogen migration occurs in path B to obtain dienone products.The closes of the five-membered ring(path C)at the subalkyl site(while the catalyst is removed),and then isomerization occurs to give the product tetrasubstituted furan.Charge analysis and IRC analysis of key intermediates and transition states are performed to verify the results.