Theoretical Studies Of Ru-Catalyzed Transfer Hydrogenative Cycloaddition And Rh-Catalyzed C-C Activation Of Cyclobutanones

Transition metal-catalyzed C-C,C-H and O-H bond activation reactions can effectively synthesize various complex ring systems,which has attracted extensive attention of organic chemists in recent years and is one of the most important and challenging fields of scientific research.In this paper,by virtue of the advantages of theoretical computational chemistry,we have studied and calculated in detail the mechanism of ruthenium?0?-catalyzed transfer hydrogenative cycloaddition and rhodium-catalyzed C-C activation of cyclobutanones based on density functional theory?DFT?,using the calculation methods of B3LYP and M06.In chapter 3,by way of theoretical calculation,we studied a strategy about theoretical Study of ruthenium?0?-catalyzed transfer hydrogenative cycloaddition of cyclohexadiene and norbornadiene with 1,2-diols to form bridged carbocycles.This synthetic strategy has high exo-and diastereoselectivity.In the present work,the possible catalytic mechanisms and origin of the exo-and diastereoselectivity for cyclohexadiene and norbornadiene were studied in detail by density functional theory calculations.The theoretical results indicate that the exoselective pathway for the cyclohexadiene substrate proceeds by a novel two-step successive C-C coupling,while the endoselective pathway undergoes the C-C coupling reaction in a conventional concerted manner.The origin of the preferential chemoselectivity of dione-cyclohexadiene C-C coupling over aromatization to benzene was investigated.Aromatization to benzene is unfavorable because of the large distortion energy of the three-membered ring in the transition state of hydrogen migration.From distortion/interaction analysis,for norbornadiene,the distortion energy plays the main role in determining the exoselectivity.In chapter 4,the mechanism of rhodium-catalyzed C-C activation of cyclobutanones:origin of ligand-controlled product selectivity was studied.Cyclobutanone C-C activation with a Rh?I?catalyst has great potential for the synthesis of fused-and bridged-ring systems.However,this synthetic application is greatly limited because of the direct CO extrusion from cyclobutanone,which leads to formation of cyclopropane as a byproduct.Through theoretical calculation,we analyzed the reasons for chemical selectivity at the molecular level,explaining why PMe₂Ph and XPhos ligands can prevent cyclopropane formation for C2-and C3-substituted cyclobutanone,respectively.More importantly,we enriched ligand computationally to exemplify how to develop new ligands.The small monodentate or bidentate phosphine ligand can favor[4+2]cycloaddition over cyclopropanation in the C2-substituted cyclobutanone system.For the C3-substituted cyclobutanone system,[4+2-1]cycloaddition is favored and cyclopropanation can be avoided when the large monodentate phosphine ligand is present.The different ligand requirements for C2-and C3-substituted cyclobutanones are attributed to different mechanisms.