Methodology Research On Rhodium(Ⅲ)-catalyzed Esterification Of 8-quinolinecarbaldehyde Derivatives

The skeleton of quinoline is widely distributed in many natural products,and many of them have outstanding biological activity.When the traditional esterification method is used to complete the esterification of the aldehyde group in the aryl-formaldehyde compounds,generally speaking,the requirements for the reaction conditions were relatively sever,and hardly to obtain the esterified products by one-step reaction.Additionally,the method of one-step reaction for preparing esterified product from 8-quinolinecarbaldehyde has not been reported yet.In order to explore the method of esterification of 8-quinolinecarbaldehyde through one-step reaction under mild conditions,we turned our attention to the study of trivalent rhodium metal catalysts which were provided with higher catalytic efficiency.For this reason,we first explored the esterification of the aldehyde group in C-8position of 8-quinolinecarbaldehyde under different reaction conditions.By screening the most suitable reaction conditions including temperature,solvent,catalysts and ligands,we found that under room temperature in THF,when use（Cp*RhCl₂）₂ as catalyst,AgSbF6 as ligand,8-quinolinecarbaldehyde can react with methanol to produce methylquinoline-8-carboxylate.Furthermore,in order to explore the scope of substrates’ application,we extended substrates under the above conditions,and the other four aldehyde substrates c8,c9,c10,c11 were prepared on the basis of six aldehyde substrates in the laboratory.Then we use these 8-quinolinecarbaldehyde compounds react with different alcohols.As anticipated before,a series of methylquinoline-8-carboxylate compounds were obtained under mild reaction condition with the yield of 40%-75%.At the same time,we use aryl aldehydes（1,2,3,4,5a）instead of 8-quinolinecarbaldehyde substrates for the substrate expansion experiment.Unfortunately,the desired ester products were not obtained,but it was accidentally found that under the reaction system,N-p-toluenesulfonyl-4-methyl-2-aminobenzaldehyde（5a）could turned into the compound likely phenylacetonitrile 5b with the yield of 70%.Because of the time and so on,deeply investigation of this kind of reaction was not conducted,and it’s mechanism also needs to be explored.With respect to the methodology in this thesis,it will be found that8-quinolinecarbaldehyde derivatives which contained different substituents couldproceed esterified reactions with alcohols when trivalent rhodium complex（Cp*RhCl₂）₂ performed as the catalyst in the system.In some degree,the fact that this method can be utilized in substrates’ esterification presents the applicability on all kinds of 8-quinolinecarbaldehyde derivatives.In the meanwhile,the reaction also has limitations,such as trivalent rhodium reagent is expensive,the substrate is only suitable for 8-quinolinecarbaldehyde derivatives,the reaction requires no water and oxygen,etc.Besides this,speculation about the possible reaction mechanism was carried out.It is worth noting that the reaction method depicted in this thesis has certain application value,and also enriches the activation reactions of C-H bond catalyzed by trivalent rhodium.