Construction Of Metal-organic Frameworks/Linear Polymer And Its Application In Aldol Reaction And Deacetalization-knoevenagel One-pot Tandem Reaction

The aldol reaction is one of the most powerful strategies for the construction of carbon-carbon bonds in organic synthesis.The stereoselectivity of this reaction has been a challenging and long-lasting task for synthetic chemists.Initially,L-proline was employed as a model chiral monomer because of its well-documented powerful asymmetric catalytic performance in aldol reaction.Considering its ready availability and low price,it is obvious that L-proline would be the first choice catalyst for preparing aldol adducts with high diastereo-and enantioselectivity.However,proline presents some major drawbacks,including poor performance in direct aldol reactions with aromatic aldehydes,limited solubility and reactivity in nonpolar organic solvents,and side reactions that make using high catalyst loadings necessary to reach satisfactory conversions.Therefore,a kind of novel catalytic systems which would improve the conversion rate and the diastereo-and enantioselectivity of the reaction was built.A novel strategy for the rational design of highly porous,linear and tightly interwined MOFs/chiral polymer composite catalysts(MIL-101-PP1 and MIL-101-PP2)was disclosed.This strategy featured a convenient in situ polymerization of pre-impregnated chiral monomers within MOFs,providing composite heterogeneous catalyst with catalytic activity superior to its homogeneous and heterogeneous analogues in catalyzing the asymmetric direct Aldol reaction in terms of diastereo-and enantioselectivity.MIL-101-PP1,with 5 mol % of catalyst loading,efficiently catalyzed this reaction to give the desired product in a good yield(91 %)with excellent diastereoselectivity(anti:syn = 12:1)and enantioselectivity(92 % ee),which is superior to that of MIL-101-PP2 with good yield(86 %),diastereoselectivity(5.6:1 dr)and enantioselectivity(84 % ee).This work highlighted the utility of cooperative effects between highly porous MOFs and easily swollen chiral linear polymer in enabling highly efficient and stereoselective asymmetric reaction.By using the similar strategy,a novel “site-isolation” methodology via convenient in situ polymerization of hostile vinyl monomers within MOFs to afford incompatible acid-and base-functionalized MOFs/polymer composites was disclosed.The excellent catalytic performance of the newly engineering MOFs/polymer composites was demonstrated in sequential two-step deacetalization-Knoevenagel reaction in a one pot.The mixture of PBSA/MIL-101 and PDMAP/MIL-101(PBSA~PDMAP/MIL-101)in equiv.catalytic amount(5 mmol %)efficiently catalyzed this reaction to give the desired product in a quantitative yield.In addition,reusing these two kinds of novel catalyst systems didn't significantly reduce their catalytic activity.Besides,these two catalyst systems had certain selectivity for the size of the substrate which would broaden the scope of its application in the field of catalysis.