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1. Ene reaction
Alder ene reaction.
Alkene with enophile and alkene with allylic hydrogen.
Formation of one new C-C and C-H bond.
No ring formation .
Mainly similar features of D.A reaction.

2. Enophile
Can also be aldehyde, ketone and imines.
The product in this case is hydroxlated.

3. Ene reaction
Can be catalyzed by lewis acids to increase the electrophilicity
of enophile.
Intramolecular ene reaction.

4. Carbonyl Ene reaction
Carbonyl compounds are good enophiles.
L.A catalysis is possible (lowering LUMO energy)
Using L.A enhances stereoselectivity.

5. Diels-Alder reaction
Method for synthesis of 6-membered ring.
One step concerted reaction
Termed [4+2] cycloaddition reaction where 4π and 2π
electrons react.

6. Diels-Alder reaction
Discovered by O.Diels and K.Alder in 1928.
Occur between a conjugated diene and substitutes
alkene to form cyclohexene ring system.
Concerted reaction can be accelerated by heating or
using some catalysts.
[4+2] cycloaddition reaction.
In retro Diels-Alder reaction trhe six membered ring is
break down to regenerate the diene and di-enophile
using high temperature usually.
Stereoselective reaction

7. Diels-Alder reaction
Stereo-specific reaction; reactants can keep their
stereochemistry.
No transition states or changed intermediates.
All elctron moving in time to from two new σ bonds.
If one or more of diene or dienophile atoms are carbon the
reaction is hetero-Diels-Alder reaction.

8. How it works?
Concerted reaction via aromatic transition state.
There are two approches, the first depends on the
interaction between HOMO of the diene and LUMO of the
dienophile.
The second depends on +I, -I groups affect since they form
negative and positive chareges on the diene and dienophile.

9. Frontier orbital interaction in the π4s+π2s
cycloaddition

10. Regioselectivity
LUMO –LUMO interaction
HOMO – LUMO interaction

11. Thermal [2+2] Cycloaddition
Mainly via ketene chemistry.
Formation four membered ring.
Alkene with electrophilic alkene .

12. Frontier orbital interaction in the π2s+π2s
cycloaddition
Thermal reaction

13. Thermal [2+2] Cycloaddition
Cyclopentadiene can react in [2+2] fashion faster than
Diels-Alder.