![]() ![]() The dienophile has two nitriles attached to it both of which are electron withdrawing. Since the two nitriles in the dieneophile are cis to each other the the two nitriles will be cis to each other in the product.Ī particularly rapid Diels-Alder reaction takes place between cyclopentadiene and maleic anhydride. Cyclopentadiene is held in the required s-cis configuration so it will make a good diene for a Diels-Alder reaction. Maleic anhydride is also a very good dienophile, because the electron-withdrawing effect of the carbonyl groups causes the two alkene carbons to be electron-poor, and thus a good target for attack by the pi electrons in the diene. Because the diene already contained a ring the product will be bicyclic. The diene is locked into an s-cis configuration which will promote the reaction. The ring portion of the diene will act as electron donating groups which will also promote the reaction. Predict the product of the following reaction: Start by rotating the diene until it is in the s-cis conformation then point it towards the double bond of the dienophile. Remove the double bonds present in the diene and dieneophile. Connect carbons 1 and 4 of the the diene to a carbon in the dienophile double bond using a sigma bond to create a six-membered ring. Create a double bond between carbons 2 and 3 of diene.ĭetermine if any substituents attached to either the double bond of the dieneophile or carbons 1 and 4 of the diene have a cis/ trans conformation. If so make sure the substituents have the same configuration in the cycloalkene product. Predicting the Product of a Diels-Alder Reaction Diels-Alder reactions with cyclic dienes favor the formation of bicyclic structures in which substituents are in the endo position. Preference of the endo position is also a facet of the suprafacial nature of the Diels-Alder reaction. The orbital overlap required for the reaction is greater when the dienophile lies directly underneath the diene.Īlkynes can also serve as dienophiles in Diels-Alder reactions: The endo position on a bicyclic structure refers to the position that is inside the concave shape of the larger (six-membered) ring. As you might predict, the exo position refers to the outside position. The words endo and exo are used to indicate relative stereochemistry when referring to bicyclic structures like substituted norbornanes. The trans relationship of the cyano groups in the dienophile is preserved in the six-membered ring of the adduct.Īnother facet of the stereochemical retention of the dienophile is that only the endo product, rather than the alternative exo product, is formed. This stereospecificity also confirms the concerted nature of the Diels-Alder mechanism. The drawing below illustrates this fact for the reaction of 1,3-butadiene with (E)-dicyanoethene. The retention of stereochemistry is due to the planar nature of both reactants and that the forming process is suprafacial (i.e. ![]()
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