Substituent Effects on Reaction Rates of Diels-Alder Reactions

2 Substituent Effects on Reaction Rates of Diels-Alder Reactions [Pg.661]

Cyclopentadiene is such a reactive 1,3-diene that it undergoes Diels-Alder reactions with all cyano-substituted ethenes. The rate constants of these cycloadditions (Table 15.1) show that each cyano substituent increases the reaction rate significantly and that geminal cyano groups accelerate more than vicinal cyano groups. [Pg.661]

Diels-Alder reactions of the type shown in Table 15.1, that is, Diels-Alder reactions between electron-poor dienophiles and electron-rich dienes, are referred to as Diels-Alder reactions with normal electron demand. The overwhelming majority of known Diels-Alder reactions exhibit such a normal electron demand. Typical dienophiles include acrolein, methyl vinyl ketone, acrylic acid esters, acrylonitrile, fumaric acid esters (irans-butenedioic [Pg.661]

Diels-Alder reactions also may occur when the electronic situation of the substrates is completely reversed, that is, when electron-rich dienophiles react with electron-poor dienes. [4+2]-Cycloadditions of this type are called Diels-Alder reactions with inverse electron demand. 1,3-Dienes that contain heteroatoms such as O and N in the diene backbone are the [Pg.662]

Stabilizing frontie. .. electron demand r orbital interactions in the. .. normal... NC CN transition states of Diels-A. .. unbalanced... II 1 re., + 1 lder reactions with. .. inverse. .. C02Me ii N N i.e +11 1 ph y C02Me [Pg.664]