Diels-Alder Rxn Stereochemistry
1
2
3
4
Diene
Dienophile
Reflux
High BP Solvent
(110oC)
5
6
5
4
3
2
1
6
(Click “Slideshow” to Animate)
6-Carbon Ring
(Cyclohexene)
Nobel Prize in Chem. 1950
First we’ll look at a simple Diels-Alder Reaction that has no Stereochemistry.
Diels-Alder Rxn Stereochemistry
1
2
3
4
5
6
Diene
Dienophile
Out
Out
Cis Dienophile
Out, Out
Cis Prod.
Cis Prod.
Cis Prod.
Cis Prod.
Cis Prod.
Cis Prod.
1
2
3
4
5
6
Not Mirror Images
Diastereomers
Same MF
Non-Superimposable
Same Connectivity
Achiral Diene
Achiral Dienophile
Meso
Achiral Product
Meso
Achiral Product
Achiral Reactants
Achiral
Product Mixture
Achiral
Solvent
Reflux
High BP Solvent
(110oC)
=
=
Nobel Prize in Chem. 1950
Now to add Stereochemistry…
Diastereomers
Pancake Flip
Diels-Alder Rxn Stereochemistry
In, Out
Alkyne
Trans
Trans
Trans Prod.
Out
In
Will not make Stereocenters
Achiral Diene
Achiral Dienophile
Achiral Reactants
Achiral
Solvent
Chiral Product
Achiral
Product Mixture
Chiral Product
50%
50%
Enantiomers
Racemic Mix.
Diels-Alder Rxn Stereochemistry
In, Out, In, Out
Trans Dienophile
Trans
Trans
Will not make Stereocenters
Trans Prod.
Racemic Mixture of Enantiomers
Rotate Diene to visualize mechanism better.
Diels-Alder Rxn Stereochemistry
=
=
In, In
Trans
Cis
Trans
Cis
Trans
Racemic Mixture of Enantiomers
Diels-Alder Rxn Stereochemistry
Endo
Exo
Major
Minor
1
2
3
4
5
6
1
2
3
4
5
A
6
B
A
B
Unequal Mixture of Diastereomers
Rotate Diene and Dienophile to visualize mechanism better.
Achiral
Diene
Achiral
Dienophile
Achiral
Solvent
Both Products Meso
Both Achiral
Achiral
Reactants
Achiral
Products
Diels-Alder Rxn Stereochemistry
In, In
Trans
In, In
Trans
In, In
Trans
This Ketone
is Endo
This Ketone
is Endo
This Ketone
is Exo
This Ketone
is Exo
Neither Product is overall Exo or Endo
Racemic Mixture of Enantiomers
Achiral Reactants → Achiral Product Mixture