Synthesis And Mechanism Analysis Of Pyrancoumarins And 5-chromotenone

Pyranocoumarins as a derivative of coumarin with such framework often exhibit biological activities.It is widely found in various medicinal plants in nature,especially it has important biological activities such as anti-inflammatory,antibacterial,anticoagulant and insecticidal.Furthermore,5-chromoenone is also the core structure of some important components of medicinal plants and thus has high economic value.Hence,the design of simple and practical synthesis methods of pyrancoumarins and5-chromoenone has been pursued by chemical researchers in recent years.In this thesis,using isoprene as the base stock,the products pyrancoumarins and5-chromoenone could be obtained respectively.The protocol has the advantages of simplicity and high atomic economy.The specific contents are listed as follows:In the first part,pyrancoumarin was synthesized from4-hydroxycoumarin and isoprene.4-Hydroxycoumarin as a common starting material or intermediate for the synthesis of pyrancoumarin compounds can be produced in an industrialization.Isoprene is an important C₅ conjugated diene in industry that can be alternatively produced by fermentation of renewable feedstock.In this part of the study,the synthesis method we proposed has achieved the conversion of cheap and readily available raw materials to high value-added compounds.With Br?nsted acid2,4-dinitrobenzenesulfonic acid as catalyst,1,4-dioxane as solvent,and reaction temperature of 90°C,pyrancoumarin was obtained with high regioselectivity of 81%yield.However,Lewis acid trifluoromethanesulfonate is used as a catalyst and 1,2-dichloroethane is used as a solvent to obtain main product pyranochromones.Then the reaction effects of different substrates were investigated indicating that this reaction has good substrate applicability.Finally,the possible reaction mechanism was further verified and proposed by reasonable experimental design and analysis.In the second part,we utilized the reaction of 1,3-cyclohexanedione with isoprene to obtain the[3+3]cyclization product.Under the reaction conditions:solid acid Nafion?10 wt%?was used as catalyst,1,2-dichloroethane as solvent,and the reaction temperature was 110 ^oC resulted in product 5-chromoenone was obtained by this method with a one-step yield of82%.Alternatively,using prenol as the substrate with the Lewis acid Al Cl₃ as the catalyst and 1,2-dichloroethane as solvent at 70 ^oC can resulted in the exclusive O-prenylation of 1,3-cyclohexanediones.Additionally,it is indicateed that both catalytic systems have good substrate application range.Finally,the possible reaction mechanism is also proposed.