Theoretical Study On Copper-catalyzed Cyanoboration Of Olefins And Aerobic Epoxidation Of Allyl Alcoho

Compared with palladium,rhodium,iridium and other precious metals,copper is relatively cheap and easy to obtain,and has lower toxicity.In addition,the valence of copper can change in either single or double electrons,which makes copper catalyst not only realize some traditional transition-metal-catalyzed reactions,but also realize free radical reactions.Therefore,copper-catalyzed reactions have great development potential.On the other hand,unsaturated hydrocarbons are one of the most easily prepared raw materials in the petrochemical industry.The methodology research using unsaturated hydrocarbons as reactants are compatible with the existing chemical production chains.In recent years,many important advances have been achieved in the researches of the functionalization of olefins and allenes catalyzed by copper,such as the epoxidation of olefins and the functionalization of allenes,which provide effective synthetic methods for obtaining value-added chemicals.However,compared with the rapid development of methodology researches,the researches on the mechanism of related reactions lag behind,and the core mechanistic questions such as the mechanistic details of elementary steps,the determining factors of rate and selectivity are difficult to solve.In this paper,the recent progress of copper-catalyzed epoxidation and boration of olefins was reviewed firstly,and then the mechanisms of copper-catalyzed cyanoboration of non-terminal allenes and aerobic epoxidation of allylic alcohols were systematically studied by using density functional theory calculations.The relevant research conclusions are as follows:(1)The calculation study shows that the copper catalyzed cyanoboration reaction of non-terminal allene with bis(pinacol)diboron reagent B2(pin)2 and N-cyano-N-phenyl-p-toluene-sulfonamide(NCTS)proceeds through the migration of allene into Cu-B bond,the cyano nucleophilic addition of allyl copper complex to the cyano of NCTS,β-nitrogen elimination,proton transfer of methanol and transmetallation of B2(pin)2.Among these steps,nucleophilic addition on cyano is the regio-and stereo-determining step,while the transmetallation is the rate-determining step.The nucleophilic addition of Cu(Ⅰ)and Cu(Ⅱ)complexes goes through the innerand outer-sphere mechanisms,respectively.When P(o-tol)3 is used,the selectivity of the inner-sphere nucleophilic addition is mainly controlled by electronic effect,and the electron-rich allylic position is favored;When Xantphos is used,the selectivity of the inner-sphere nucleophilic addition is mainly affected by steric effect and π-πstacking effect,while the selectivity of the outer-sphere nucleophilic addition is mainly controlled by the conjugation of olefins and aryl substituents.(2)The computational study on the aerobic epoxidation of allylic alcohol catalyzed by copper indicates that the catalyst precursor Cu(OAc)2 is not an active catalyst,and it needs to in situ generate active CuOAc complex by the deprotonation of alcohol O-H bond,β-carbon elimination,dissociation of carbon radicals followed by hydrogen atom transfer with 1,6-dioxane solvent,peroxidation of solvent carbon radical,epoxidation of alkene by alkyl peroxy radical and decomposition of radical 2-(λ1-oxidanyl)-1,4-dioxane.CuOAc complex activates dioxygen to form a dinuclear Cu(Ⅲ)-oxo intermediate,which accomplish the epoxidation of olefins in a concerted mechanism with generating dinuclear Cu(Ⅱ)-oxo complex,and this step is the rate-determining step.The epoxidation of the second olefin goes through a stepwise mechanism involving spin state change.When tetrahydrofuran is used as solvent,the corresponding radical 2-(λ1-oxidanyl)tetrahydrofuran is more likely to undergo the side reaction of hydrogen atom transfer with allylic alcohol and hinders the epoxidation reaction.Through the above theoretical calculations and research,we have elucidated the detailed mechanisms of copper catalyzed cyanoboration reaction of non-terminal allene and aerobic epoxidation of allylic alcohol reaction,revealing the reaction ratedetermining step and selectivity determining step as well as their regulatory mechanisms,especially in terms of the structure activity relationship related to the valence state of copper catalysts and the aerobic conversion of copper complexes with different valence states,providing more in-depth mechanistic insights.The design of subsequent reactions can generate theoretical guidance value.