SolutionsDiels-Alder Cycloaddition
1. Table of adducts
Draw the structures of all the Diels-Alder adducts obtained when each diene (horizontal) reacts with each dienophile (vertical).
2. A reactive diene?
Which of these dienes does not undergo the Diels-Alder reaction? a) 1,3-butadiene; b) (2Z,4Z)-2,4-hexadiene; c) cyclopentadiene; d) 2,3-dimethyl-1,3-butadiene.
(2Z,4Z)-2,4-Hexadiene reacts very poorly: in the s-cis conformation needed for the reaction, the two inner methyl groups clash.
Cyclopentadiene is very reactive because its s-cis conformation is locked by the ring; at room temperature it dimerizes.
3. Electron demand
Order by reactivity towards 1,3-butadiene: ethylene, methyl acrylate and maleic anhydride.
Maleic anhydride > methyl acrylate > ethylene. The more withdrawing groups the dienophile has, the lower its LUMO and the better it interacts with the diene HOMO (normal electron demand).