Intramolecular Diels-Alder reaction

(E)-3-Methyldeca-1,3,9-triene

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Sn2

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

There is no conjugating group on the alkene to stabalise the transition state by overlap between the orbitals of the conjugating group and the back of the diene - the reaction is only able to occur because it is intramolecular.

Because of this there is no endo effect - the molecule simply folds up in the most sterically favourable way, leading to the trans ring junction. Where the alkene has a conjugating group, the endo product may be formed.

Intramolecular Diels-Alder reactions may, or may not, give endo, exo or a mixture of products.

Be prepared!

 

 

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