Diels Alder Reaction

Question

Draw structural formulas for the diene and dienophile that combine in a Diels-Alder reaction to form the product shown.

Diene

+

Dienophile

1. Consider E/Z stereochemistry of alkenes.
2. Draw one structure per sketcher. Add additional sketchers using the drop-down menu in the bottom right corner.
3. Separate multiple products using the + sign from the drop-down menu.

Answer 1

Hi Anna,

Please see my answer above and explanation here. If you have any more specific questions about why the above occurs, please let me know.

In Diels-Alder, new bonds form between a diene (a molecule with conjugated [alternating] pi bonds) and a different molecule with at least 1 pi bond (the dienophile). The new bonds and final structure occur due to the interaction of the pi-bonds present in the original molecules.

The suffix '-ene' (as in Alkene) indicates a molecule with at least one double bond, so a diene has 2 double bonds.

Whenever your diene is cyclic, you'll end up with a bridge structure as part of a new 'bi-cyclic' molecule as the product of the Diels-Alder reaction. If you imagine bending upward just the part of the pentadiene molecule that is not part of the conjugated pi bond system, it may help visualize how the bridge structure forms while the new bonds created during the reaction form underneath the bridge.

The other molecule in the reaction, the dienophile, must contain at least one pi (double or triple) bonded carbon. Since pi-bonded carbons cannot rotate, substituents attached to the double-bond are fixed in their positions relative to all other atoms in the given molecule. In this case, the substituents bonded to one of the double-bond carbons of the dienophile are chlorine and a nitrile (a CN triple bond). There are hydrogens bonded to the other double-bond carbon, but since these are both the same atom they do not need to be drawn and differentiated stereochemically.

Once the reaction occurs, the substituents remain fixed and on opposite faces of the ring that forms, so the chlorine and nitrile must be drawn with wedged/dashed lines to show that they remain fixed in their positions relative to the rest of the atoms in the new molecule.

I also pasted links to a site that lays out the mechanism of the Diels-Alder. Their diagrams may help clarify how the dienophile and diene interact better than I can with words. The site (masterorganicchemistry.com) is a great option for reading up on any O chem topic.

https://www.masterorganicchemistry.com/2017/08/30/the-diels-alder-reaction/

https://www.masterorganicchemistry.com/2017/09/08/cyclic-dienes-and-dienophiles-in-the-diels-alder-reaction/