Diels-Alder reaction Introduction – Identifying a Diels-Alder Reaction

Cyclopentadiene and Nitroethylene(nitroethene)


Click the structures and reaction arrows in sequence to view the 3D models and animations respectively

Diels-Alder reactions are cycloadditions which occur between a diene and a conjugated alkene, known as the dienophile.

Two sigma bonds are formed or broken in one concerted step – there are no intermediates at all. This type of reaction is known as a pericyclic reaction. As seen above, the endo transition state leads to the nitro group being opposite the CH2 bridge – for more information about endo and exo see this page.

Recognising a Diels-Alder product is easy. Look for a six membered ring with a double bond inside the ring and a conjugating group outside the ring on the opposite side to the double bond.

J. Sauer, Angew. Chemie Int. Ed. English, 1966, 5, 211–230.



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