Construction Of Lewis Acidic Metal-organic Frameworks And Their Catalytic Intramolecular Diels-Alder Reactions For The Synthesis Of Renewable Isoindoline-1-one

Isoindolin-1-one is a common structural motif in drugs and natural products,but the traditional methods of isoindolin-1-one skeleton synthesis are not sustainable because the source of aromatic chemicals relies heavily on fossil resources.As a relatively stable renewable resource,biomass is the only renewable carbon resource that can replace fossil carbon and upgrade into fuel and chemicals.Diels-Alder/aromatization of furan platform molecules from biomass conversion is an effective strategy to obtain 100%atom-economical renewable aromatics,but an effective catalyst is needed to promote the efficient reaction.In this paper,zirconia chloride and hafnium tetrachloride were used to provide metal ions,and homophenic acid as organic ligand,and then Lewis acid metal-organic frame materials were prepared by solvothermal method.Lewis acid metal-organic framework materials were used to catalyze the intramolecular Diels-Alder cycloaddition of furan rings and monoolefine.The obtained Diels-Alder ring adduct was synthesized into isindoline-1-one by dehydration aromatization catalyzed by ionic liquid[Bmim]HSO₄.The catalytic synthesis pathway is green,efficient and economical.（1）In this paper,Zr OCl₂·8H₂O and H₃BTC were used as raw materials to prepare Zr-BTC catalyst by solvothermal method,which was used to catalyze the intramolecular Diels-Alder cycloaddition reaction between furan rings and mono-olefin.The catalyst characterization shows that Zr-BTC is an octahedral porous material with excellent surface area and high Lewis acidity.Diels-Alder cyclic adduct 3a had the highest yield（91%）and the highest catalytic activity（15 mg）in DMSO（3 m L）at 100℃for 5 h.Kinetic studies show that Zr-BTC catalyst can effectively reduce the reaction activation energy of 15.85 KJ/mol.Finally,the obtained Diels-Alder cycloadduct was almost completely dehydrated by acidic ionic liquid[Bmim]HSO₄（reaction condition:80℃,2 h）to obtain 99%isoindoline-1-ketone 5a.[Bmim]HSO₄（2 m L）catalyzed the dehydrating aromaticity of Diels-Alder ring adjuncts.The mechanism of dehydrating aromaticity of Diels-Alder ring adjuncts shows that the process mainly includes ring opening protonation of bridging ether and C-O bond cleavage.（2）The Hf-BTC catalyst was prepared by using Hf Cl₄ instead of Zr OCl₂·8H₂O,and the catalyst was used to catalyse the intramolecular Diels-Alder reaction of compound 3a.The catalyst characterization shows that Hf-BTC has similar morphology to Zr-BTC,and has higher specific surface area and total acid content than Zr-BTC.The catalyst activity test showed that the yield of the intramolecular cyclic adduct 4a reached 98%at 100℃,DMSO（3 m L）and 5 h.Kinetic studies show that Hf-BTC catalyst can effectively reduce the apparent activation energy of 17.13 KJ/mol.Finally,the possibility of synthesis of isoindoline-1-ketone 5a catalyzed by one-step intra-molecular DA/dehydration aromatization of several commercially available zeolites,Zr-BTC or Hf-BTC and[Bmim]HSO₄ was investigated.It was found that 3a could be converted to isindoline-1-ketone 5a at 79%and 83%yields under the catalysis of Zr-BTC or Hf-BTC and[Bmim]HSO₄,respectively.