Small Organic Molecules Catalytic Olefin And Amine The Study Of The Theory Of The Asymmetric Reactions

Asymmetric organocatalysis has been an important tool for building themolecular scaffold, which plays an important role in the fields of chemistry, pharmacy,materials and so on. Chirality is one of the existent characters in nature. Manycompounds, acting as the foundation of life activities, are almost chiral. Recently,asymmetric reactions of alkenes and amines catalyzed by small organic moleculeshave obtained widespread attention and have made great progress. Currently, chiralsmall molecules have become important catalysts in asymmetric catalysis for easypreparation and high catalytic activity. Using chiral compounds as catalysts not onlycan promote the reaction but also can cause higher enantioselectivity, which leads thedramatic development of asymmetric catalysis. Small molecules can offer manyadvantages in organic synthesis. The study on the mechanism of asymmetric reactionsfrom the molecular level could facilitate understanding of reaction process andexplaining the experimental phenomenon. In addition, finding out the activation ofdifferent organocatalysts and revealing the role of catalysts can provide theoreticalguidance for the development of new catalysts.In this paper, the alkene hydroaminations and asymmetric michael additionreactions catalyzed by two typical chiral organic catalysts were studied in detail usingDFT calculations. From microscopic angle, this paper uncovers the mechanisms ofasymmetric synthesis reactions and reveals the special nature of the catalysts.The main research contents and conclusions are as follows:The mechanism of alkene hydroaminations catalyzed by chiral aldehyde throughtemporary intramolecularity has been investigated using density functional theory.The mechanism of alkene hydroamination reaction is divided into two parts to bediscussed. The first part is a stepwise dehydration process involving a hemiaminalformation. It affords the nitrone catalyst though rapid intermolecular nucleophilicaddition of benzylhydroxylamine to chiral aldehyde precatalyst. In the second part,nitrone undergoes an attack of allylamine from different faces. Then a catalytic cycle occurs through an aminal formation—hydroamination—ring opening—productrelease process. Four enantioselective pathways of S and R structures arecharacterized with nitrone catalyst. Enantioselectivity is attributed to the differentforming ways of a planar five-membered ring. Re-2a and Si-2b are the preferredpathways for the S3and R3products, respectively. We have also analyzed the addedcompetitive reactions. The present DFT study provides the details of the reactionmechanisms. The results will stimulate not only the development of the new alkenehydroaminations but also the expansion of the scope of chiral aldehydes.Based on density functional theory calculations, we have studied aquinine-derived thiourea-tertiary amine bifunctional catalyst catalyzed Michaeladdition of α-substituted-α-nitrophosphonates to nitroolefins. According to ourcalculated results, the stereoselectivity of the reaction is controlled by C-Cbond-forming step. The complexes formed by the catalyst and nitroolefin enhancedthe eletrophilicity of β-C atom of the nitroolefin and favored nucleophilic attack of thenitrophosphonate. At the same time, we also verified the experimental results andexplained the main product of the anti-product. Four enantioselective pathways arecharacterized in detail. The results we obtained is in agreement with the experimentalfact. The present DFT study provides the details of the reaction mechanisms andexplains the experimental results well. The calculated results not only deepen theawareness of the catalytic mechanism with bifunctional catalysts but also providetheoretical guidance for the design of new organic catalysts in the asymmetricMichael addition.