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首页> 外文期刊>Bulletin of the Chemical Society of Japan >Origin of the Endo/Exo Stereoselectivity and Syn/Anti Face-Selectivity in Diels-Alder Reactions,Determined by Transition State Energy Partitioning
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Origin of the Endo/Exo Stereoselectivity and Syn/Anti Face-Selectivity in Diels-Alder Reactions,Determined by Transition State Energy Partitioning

机译：过渡态能量分配确定的Diels-Alder反应中内/外立体选择性和Syn /反面选择性的起源

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摘要

The origins of stereo- and face-selective Diels-AIder reactions of 5-substituted 1,3-cyclopentadienes(CP)with some dienophiles were elucidated by means of semiempirical PM5,DFT(B3LYP),and ab initio RHF methods.The activation energies by the improved PM5 and B3LYP/6-31+G(d)methods were in good agreement with the experimental results.We partitioned the activation energy(DELTAE_(act))into diene deformation(DELTAE_(df-dien))and dienophile deformation(DELTAE_(df-dphil)),and the diene-dienophile interaction(E_(int))energies,in addition to the new intrinsic reaction coordinate(IRC)energy(DELTAE_(irc))partitioning.Such analysis revealed the major factors in the determining endo/exo and syn/anti se-lectivities of the reactions of 5-substituted CP.The syn-selectivity of the 5-F-CP is explained by the lower DELTAE_(act)(2-3 kcal/mol)caused by relatively smaller DELTAE_(df-dien),which leads to slighter repulsion between the reactants.This low activation energy is inferred to be caused by the better second orbital interaction or intramolecular orbital interactions between the diene pi and fluoro-substituent n orbital moieties,as well as by better intermolecular Ji-n orbital interactions between the diene-pi and dienenophile-pi moieties.On the other hand,the anti-selectivity of the methyl substituted CP mainly appears from bigger E_(df-dien)in the syn-isomer.A novel economical method of IRC energy partitioning to the reactants,TS intermediates andproducts is also introduced in order to verify the energy balance of other calculation methods and other reactions.
机译：通过半经验PM5，DFT（B3LYP）和从头算RHF方法阐明了5-取代的1,3-环戊二烯（CP）与一些亲二烯体的立体和面部选择性Diels-AIder反应的起源。改进后的PM5和B3LYP / 6-31 + G（d）方法与实验结果吻合良好。将活化能（DELTAE_（act））分为二烯形变（DELTAE_（df-dien））和亲二烯体形变（DELTAE_（df-dphil））和二烯-二亲亲和体相互作用（E_（int））能量，以及新的内在反应坐标（IRC）能量（DELTAE_（irc））划分。 5-F-CP的同选择性是由较低的DELTAE_（act）（2-3 kcal / mol）引起的，解释了5-F-CP的同选择性。相对较小的DELTAE_（df-dien），导致反应物之间的排斥力较小。这种较低的活化能被推测是由于甜菜二烯pi和氟代n轨道部分之间的第二轨道相互作用或分子内轨道相互作用，以及二烯pi和亲二烯体pi部分之间更好的分子间Ji-n轨道相互作用。甲基取代的CP的选择性主要来自于同分异构体中较大的E_（df-dien）。还引入了一种经济的IRC能量分配给反应物，TS中间体和产物的经济方法，以验证其他计算的能量平衡方法和其他反应。

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