Theoretical Studies On The Mechanisms Of Rhodium Catalyzed C-H Activation Reactions

The rhodium(III)-catalyzed C-H activation reaction is a hot topic of current organic chemistry research.It provides an effective way that converts the inert C-H bond to C-X bond.In this thesis,the mechanistic understanding of rhodium(III)-catalyzed C-H activation reactions of benzamides containing internal oxidant were studied by DFT calculation.Comparing the energies of different reaction pathways,the detailed mechanism was disclosed,which explained well the experiments.The results are significant for future research.This thesis includes the following two aspects:(1)Mechanistic understanding of rhodium(III)-catalyzed C-H activation/cycloaddition reactions of benzamides and methylenecyclopropanes(MCPs).First of all,all possible pathways for reaction of N-Pivaloxybenzamide were calculated by DFT.When the aryl is a phenyl group,the privalate migration was kinetically easier.When the aryl is a furanyl group,the β-C elimination was the most favorable reaction.The rhodium(V)-nitrenoid intermediate is involved in both reactions.If the aryl has a thiophene group,the above two types of reactions have similar energies.In addition,the reason for why N-methoxy benzamide failed to react with methylenecyclopropanes(MCPs)can be well explained by the DFT results.(2)Mechanistic understanding of rhodium(III)-catalyzed C-H activation/cycloaddition reactions of benzamides with cyclopropenes.The mechanism of substrate-dependent chemoselectivity reported by the Wang group was studied by DFT calculations.Through C-H activation and olefin insertion,seven-membered rhodacycle intermediates are formed.The results showed that the N-pivaloxybenzamide undergoes N-O bond cleavage more easily than the β-C elimination by opening of the three-membered ring,giving rise to tricyclic lactam product.However,for N-phenoxyacetamide,the β-C elimination occures more easily and forms 2H-chromene as the product.