Theoretical Study On The Mechanisms Of Cu(?)Catalyzed Allylic Alkylation And W(0)Catalyzed[4+2]Cycloaddition

Comparing with the experimental chemistry,computation chemistry is economical and can assist people with understanding chemical process essence on the molecular level.A combination of computational and experimental chemistry is a tendency in the field of chemical research.In this paper,density functional theory has been systematically performed to investigate the mechanism of copper-catalyzed allylic alkylation and tungsten-catalyzed Diels-Alder reaction.All the geometry optimization and energy calculation of stationary points in possible reaction pathways is carried on outlining potential energy surface and obtaining optimal reaction channel.Firstly,the mechanism of the Cu(I)-catalyzed allylic alkylation and the influence of the leaving groups(-OPiv,-SPiv,-Cl)on the regioselectivity of the reaction have been explored using density functional theory(DFT).A comprehensive comparison of many possible reaction pathways shows that[(i-Pr)2Cu]-prefers to bind first oxidatively to the double bond of the allylic substrate at the anti-position with respect to the leaving group,followed by the dissociation of the leaving group.When the leaving group is not taken into account,the reaction then undergoes an isomerization and a reductive elimination process to give the a-selective product or the y-selective product.When-OPiv,-SPiv,and-Cl groups are present,the optimal route for the formation of both ?-substituted products and y-substituted products change from the stepwise elimination to the direct process,in which the leaving group plays a stabilizing role for the reactant and destabilizes the transition state.The difference to the energy barrier for the a-and y-substituted products is 2.44 kcal/mol with-SPiv,2.33 kcal/mol with-OPiv,and 1.98 kcal/mol with-Cl,respectively.This suggests that a-regioselectivity in the allylic alkylation follows a-SPiv>-OPiv>-Cl trend,which is in good agreement with experimental findings.This trend mainly originates in the difference between the attractive electrostatic forces and the repelling steric interactions of-SPiv,-OPiv,and-Cl groups on Cu.Secondly,the density function theory also have been carried on investigation of Diels-Alder reaction between 1,2-dihydropyridine and methyl vinyl ketone catalyzed by TpW(NO)(PMe3)and BF3 LA.The detailed mechanism researches based on four designed models reveal that this Diels-Alder-reaction was happened through the stepwise pathway TpW(NO)(PMe3)?{DHP-[W]}?3a-??IM3a/3a'-??3a'-??5-? in the ground state.The rate-limiting step with an energy barrier 28.60 kcal/mol is occurred in the first nucleophlic addition step.The presence of TpW(NO)(PMe3)mainly controls the stereo-and regioselectivity of reaction.The role of BF3 is increased the electrophilicity of MVK by means of coordination with carbonyl group.Our computational results verify that only in the presence of both TpW(NO)(PMe3)and BF3 LA,can this D-A reaction take place to exclusively yield[4+2]cycloadduct under the mild reaction condition.The experimental findings are rationalized by our computed results.