# Why do conjugated dienes undergo Diels-Alder reactions?

If conjugated dienes are so stable, why can they still undergo Diels-Alder reactions ([4+2] cycloaddition)?

• Hint: Stable does not mean unreactive. – Ben Norris Apr 3 '17 at 10:53
• Their stability is to be balanced against the conditions they are exposed to. And there are other polyenes even more stable (like benzene) than dienes. In addition, provided enough activation provided (some Diels-Alder reactions already occur at room temperature, for example cyclopentadiene reacting with itself), do not forget to compare thermodynamics, like $\Delta{}_fH$ of starting material(s), on one, and the of the product(s) on the other side of the equation. – Buttonwood Apr 3 '17 at 11:19