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A Complete Guide To The Diels Alder Reaction

The Diels-Alder Reaction

In Diels-Alder reaction, two reagents: diene and dienophile react together under heat to make a cyclohexene.


Diene must be in s-cis confirmation. Both double bonds on the same side of the single bond. If it is not, molecule needs to be rotated . If the molecule can't turn into s-cis conformation, diene can not participate in Diels Alder.




Diels-Alder reaction is a concerted, one step mechanism.

The Effect of Substituents on Rate Of Diels-Alder Reaction

The rate of Diels Alder increases when electron withdrawing groups (EWG) are placed on the dienophile and electron donating groups (EDG) are placed on the diene.



STEREOCHEMISTRY


Configuration of both diene and dienophile is retained.


Diels Alder can also form bridged compounds





Under kinetic conditions, ENDO is preferred!

What this means is that when you draw the product of Dials-Alder reaction that is a bridged compound, make sure to draw the groups on the side going OPPOSITEto the direction of the smallest bridge (usually the smallest bridge is up and you need to draw the group DOWN), as shown in the picture below.


Stereochemistry of Endo product that is not bridged

Stereochemistry of Endo product
Stereochemistry of Endo product



How to predict the product of Diels-Alder when asymmetrical reagents are given

If there is an electron donating substituent on the diene and an electron withdrawing substituted on the dienophile, the product will be either 1,2 (both groups next to one another) or 1,4(groups opposite one another) but NOT 1,3 (groups one carbon away from one another).


How to predict the product of Diels-Alder when asymmetrical reagents are given
How to predict the product of Diels-Alder when asymmetrical reagents are given


How to predict the product of Diels-Alder when asymmetrical reagents are given
How to predict the product of Diels-Alder when asymmetrical reagents are given


Reverse Diels-Alder


Reverse Diels-Alder
Reverse Diels-Alder

To figure out the diene and dienophile that gave the Diels-Alder product, we must first find a cyclohexene. We then, number it according to the prototype shown above. We can show the products of the prototype with the same numbering as above and attach groups that are missing looking at the starting molecule.



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