Return to Contents Chapter 10: Conjugation in Alkadienes and Allylic Systems Ch 10 contents

Diels-Alder Reaction (Nobel Prize in 1950)

simplest Diels-Alder reaction, butadiene and ethene to cyclohexene
Diels-Alder reaction of butadiene and ethyne to 1,4-cyclohexadiene
The concerted mechanism of the Diels-Alder reaction
Dienes Common dienes
Dienophiles common dienophiles

Stereoselectivity:

a cis-dienophile gives cis-substituents in the product
(look at the two ester groups in the product)

cis dienophile

a trans-dienophile gives trans-substituents in the product.
(look at the two ester groups in the product)

trans dienophile

If the diene substituents have the same stereochemistry (here they are both E), then both diene substituents end up on the same face of the product.
(look at the two methyl groups in the product)

subs diene

If the diene substituents have opposite stereochemistry (here one is E and one Z), then the diene substituents end up on opposite  faces of the product.
(look at the two methyl groups in the product)

subs diene

Cyclic dienes can give stereoisomeric products depending on whether the dienophile lies under or away from the diene in the transition state.  The endo product is usually the major product (due to kinetic control)

endo and exo products from cyclic dienes
formation of endo product
Diene and dienophile aligned directly over each other gives the endo product 
(dienophile under or in = endo)
 
formation of exo product
Diene and dienophile staggered with respect to each other gives the exo product 
(dienophile exposed or out  = exo)
 

 

Compare the relative position of the dienophile fragment in the JSMOL images above.


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  Dr. Ian Hunt, Department of Chemistry, University of Calgary