| β-Enaminones are important intermediates for the synthesis of antispasmodic drugs,anti-inflammatory drugs,anticancer drugs and other drugs.Besides,they are often used in the synthesis of some nitrogen-containing single heterocyclic compounds or fused heterocyclic compounds.Therefore,many scientific researchers have devoted themselves to resear-ching efficient and convenient methods to prepare such compounds.The condensation reaction using amine compounds and β-dicarbonyl compounds as raw materials is the most widely used.However,amine compounds are easy to be oxidized in the air,which is not convenient for storage and transportation.Considering that amine compounds are often obtained by reduction of nitro compounds.Therefore,the development of a new and efficient cascade reaction starting from nitro compounds to prepare enaminones has attracted our attention.Unfortunately,there is a dilemma for developing such a bifunctional catalyst.The catalyst for the hydrogenation of nitro compounds requires an electron-rich environment to improve the chemical selectivity of-NO2 according to our previous results,while the condensation of amine compounds with β-dicarbonyl compounds often requires a Lewis acid type catalyst,which means an electron-deficient environment.Therefore,developing a catalyst that can reconcile the contradictory electronic effects for the catalytic hydrogenation of nitro and the insitu condensation with diketones is the key to realize the cascade synthesis of βketoenamines.Firstly,we chose p-nitrotoluene and acetylacetone as template substrates to explore the catalyst,and atmospheric pressured H2 was applied as the hydrogen source.Successfully explored and prepared the Pd-e@UiO-66 dual-functional catalyst with electron-rich Pd nanoparticles wrapped in defect-rich UiO-66,and tested and analyzed it by SEM,TEM,XPS and other characterization methods.Pd-e@UiO-66 is a nanoreactor,where the metal is wrapped inside the material,while the Lewis acid site is located outside.The two reactions are separated and do not interfere with each other,which can effectively adjust the conflicting electronic effects between nitro hydrogenation and further condensation reactions,and ensure the smooth progress of the reaction.In addition,the Pd NPs are more abundant in electrons after being modified by PVP,which is conducive to the hydrogenation reaction.Moreover,the UiO-66 crystal structure was successfully synthesized by FTIR,XRD and BET analysis,and the Pd content is only 1.73 wt%tested by ICP.The material is easy to obtain and can be used in a wide range of production.Compared with the Pd/UiO-66-NH2 catalyst with Pd nanoparticles supported on the surface of UiO-66-NH2,it has better catalytic performance.After that,we optimized the conditions of the reaction system so that the catalyst performance can be brought into full play.Under the optimal conditions,more than 30 kinds of β-enaminones have been prepared by changing the types of nitro compounds and dicarbonyl compounds,and all of them showed good catalytic performance,which proved that the catalyst had good universality.The catalytic performance of the template reaction was not significantly decreased by 5 cycles,and the template reaction was amplified by 10 times,which also showed excellent catalytic performance in the appropriate time.Finally,combined with our experiments,previous work results and reported literature,we also explained the reaction mechanism. |
