Study On The Mechanism Of Rhodium-catalyzed [5+2] Cycloaddition And Palladium-catalyzed Acetoxylation Reaction

Transition metal-catalyzed carbon-heteroatom bonds and carbon-carbon bonds are the basic and very effective methods for the preparation of natural compounds,drugs,and biomolecules in organic reactions.Transition metals are more and more favored by organic chemists as catalysts.In this article,we mainly use density functional theory to study the Rh-catalyzed[5+2]cycloaddition reaction and Pd-catalyzed the acetoxylation reaction.The main contents are as follows:1.A brief description of various experimental methods and research significance for the preparation of cyclic compounds.2.Introduce the application of ab initio self-consistent method,density functional theory,transition state theory and calculation software involved in the research of reaction mechanism in this article.3.In this chapter,the mechanism of the intramolecular cycloaddition reaction of alkynes and allylcyclopropane catalyzed by rhodium to synthesize bicyclic product 1 and cyclopentene product 2 has been calculated and studied.Two catalysts of RhCl（CO）₂and RhCl（CO）dppp have been studied.Formation of product 1 is mainly divided into three steps,oxidative addition,ring-opening reaction,and reductive elimination.The rate-determining step is oxidative addition.For RhCl（CO）₂catalyst,when the substituent R is H,the Gibbs free energy barrier is 26.1 kcal/mol;when the substituent R is TMS,the Gibbs free energy barrier is 26.7 kcal/mol.For RhCl（CO）dppp catalyst,when the substituent R is H,the Gibbs energy barrier is 26.4 kcal/mol;when the substituent R is TMS,the Gibbs energy barrier overcome is22.9 kcal/mol.Three possible reaction mechanisms for the generation of product 2 have been calculated.It is found that the optimal reaction path is mainly divided into two steps,oxidative addition and reductive elimination.The rate-determining step is reductive elimination.For RhCl（CO）₂catalyst,when the substituent R is H,the Gibbs energy barrier is31.9 kcal/mol;when the R substituent is TMS,the energy barrier overcome is 33.6 kcal/mol.For RhCl（CO）dppp catalyst,when the R substituent is H,the Gibbs energy barrier overcome is 28.6 kcal/mol;when the R substituent is TMS,the Gibbs energy barrier overcome is 32.3kcal/mol.4.The reaction mechanism of palladium-catalyzed quinazolinone-directed C（sp³）–H acetoxylation has been investigated.The mechanism A（no base）of the formation product 2a and the mechanism B（with base）of the formation product 2b has been considered.In mechanism A,two pathways（path 1 and path 2）are calculated.Through energy calculation and structural analysis,the path 1 is preferred,which mainly includes H migration,oxidative addition,and reductive elimination.The oxidative addition process（3→TS3-4→4）is the rate-determining step for the formation of product 2a along entire reaction path.In mechanism B,there are two cases according to the different coordination positions of Na atoms in sodium carbonate.The calculation results show that the favorable path mainly includes three parts:C-H activation,oxidative addition and reductive elimination.The C-H activation process（19→TS19-22→22）is the rate-determining step of the reaction.