Theoretical Study About [3+2] Cycloadditions Catalyzed By Palladium And Silver

Transition metal-catalyzed cycloaddition reactions between unsaturated compounds are one of the important ways to construct carbo-and hetero-cycles compounds.In recent years,with the continuous development and utilization of transition metal catalysts,such cycloaddition reactions have developed rapidly,and significant progress has been made in expanding the range of reaction substrates,improving reaction efficiency and selectivities.In this dissertation,two[3+2]cycloadditions catalyzed by palladium and silver have been explored by employing B3LYP density functional theory?DFT?and DGDZVP basis set.Potential energy profiles has been obtained based on optimization,which can be used to analyze microscopic reaction mechanism and supply theoretical guidance for understanding of other similar reactions and the improvement of experimental research.The whole dissertation is divided into five chapters.In Chapter 1,we briefly reviewed the research progress in the synthesis of five-membered carbo-and hetero-cycles through the[3+2]cycloaddition of cyclopropanes and other three-carbon components catalyzed by Lewis acids and transition metals.In Chapter2,we made an intruduce to related theories and computational methods.Detailed computaitonal results of palladium-and silver-catalyzed[3+2]cycloaddition reactions involving olefins were introduced in Chapters 3 and 4 respectively.Finally,a conclusion for the whole thesis was made in Chapter 5.Main computatiaonl results obtained are as follows:1.For the[3+2]cycloaddition reaction of vinyl oxiranes with olefins catalyzed by palladium catalyst,possible reaction mechanism was explored based on the theoretical calculations.The whole reaction includes two stages.The first stage is:complexation between olefin and vinyl oxirane through C-H···O weak interaction,as well as the coordination of palladium?0?/phosphine-containing ligand with alkenyl of vinyl oxirane,activates oxirane and causes its three-membered ring's opening,forming a ring-opening intermediate.The second stage is:the ring-opening intermediate undergoes a stepwise cycloaddition with olefin to form C-O and C-C bonds in sequence,forming the corresponding five-membered heterocyclic intermediate;then,the five-membered heterocyclic intermediate removes the palladium catalyst fragment to produce the final products.For the above reaction processes,we found two possible styles for the coordination of catalyst with substrate,named Path a1 and a2 respectively.On Path a1,the isopropyl of the catalyst is on the back side of the vinyl and on the left side of the entire molecule,while the two phenyl groups connected with the phosphine atom are on the right side of the molecule.On the contrary,on Path a2,the isopropyl of the catalyst faces the front side of the vinyl and is located to the right of the entire molecule,with the two phenyl groups connected with the phosphine atom on the left of the molecule.Based on comparison of free energy barriers of the rate-determining step?RDS?and the spatial structure of key transition states on the two paths,we find that Path a1 is more favorable to Path a2,that is,the first coordination mode has advantages.In addition,our computaitoanl results indicate that the step of forming C-O bond during the[3+2]cycloaddition is the diastereoselectivity-determining step,while the free energy barrier differences at the ring-closure step further increase and improve the diastereoselectivity of the reaction.Comparison of computational results derived from B3LYP?CAM-B3LYP?LC-?PBE?M06-2X and TPSSH methods show smallest derivation of CAM-B3LYP results from experimental data.2.For the[3+2]cycloaddition reaction of olefins with internal alkynes catalyzed by silver catalyst,possible reaction mechanism was speculated and verified through theoretical calculations,based on reported experimental results.The reaction also occurs through two stages.The first stage is the[3+2]cycloaddition process:Under the catalysis of silver,olefin reacts with internal alkyne to form a stepwise intermediate INT1d by forming the first C-C bond.This intermediate undergoes 1,5-hydrogen migration and ring-closure to form a five-membered carbocycle through the formation of the second C-C bond.The second stage is the continuous hydrogen migration stage.The hydrogen atom C?sp³?-H?a?on the five-membered ring undergoes two hydrogen migrations to form a new intermediate.Finally,this intermediate produces cyclopentene derivatives by getting off the silver catalyst fragment.There are two possible reaction paths?Path 1 and 2?in the second stage reaction,which corresponds to the migration of the hydrogen atom H?a?from the outside/inside of the five-membered ring,from carbon atom C?9?go to C?7?,and form the cyclopentene product and remove the catalyst finally.Since the free energy barrier of transition state on Path 1 is 9.7 kcal·mol^-1 lower than that on Path 2 during the first hydrogen migration process,and corresponding intermediate on Path 1 is also more stable than that on Path 2,Path 1 is the dominant path.The potential energy profiles of the reaction show that the ring-closure transition state TS3d of the[3+2]cycloaddition is the highest point in the figure,so the ring-closure step is the rate-determining step of the whole reaction.Finally,according to the comparison and analysis of computational results obtained by employing B3LYP,B3LYP-D3 and M06-2X methods,we find that B3LYP-D3 and M06-2X methods,which include dispersion correction are more suitable for describing this reaction system.And the study of solvent effects has further confirmed that the calculation results in solution are closer to corresponding experimental results than those obtained in gas phase.