Substituent effects in the Diels-Alder reactions of butadienes, cyclopentadienes, furans and pyroles with maleic anhydride

In this study, activation energies in the Diels-Alder reactions of a series of substituted butadienes, cyclopentadienes, furans and pyroles with maleic anhydride were calculated by the M06-2X/6-31G(d) method. The substituent effects on the reactivity and the endo-exo selectivity have been examined. The strength of reactivity effect has an order of pyroles>furans>cyclopentadienes>butadienes, which is highly correlated with the lowest unoccupied molecular orbital energy, the electronic chemical potential and the electrophilicity of parent diene but relatively less correlated with the highest occupied molecular orbital energy and chemical hardness. The trend that an increase of necleophilicity caused by an electron-donating group on the diene favors the endo TS is effective with C2 substitution. With C1 substitution, the trend is ambiguous or even opposite. Copyright (c) 2015 John Wiley & Sons, Ltd.