Diels-Alder reaction
Mechanism for the diels-alder reaction
- Diels-Alder reaction is a [4 + 2] cycloaddition.
- The reaction proceeds between a diene and a dieophile.
- The latter compound is called a dienophile because it “loves a diene”(Δsignifies heat🔥).
- The reaction is a concerted reaction: the addition of the electrophile and the nucleophile occurs in a single step.
Conformations of the Diene
The conjugated diene
There are two different planar conformations: an s-cis conformation and an s-trans.
The s-trans conformation is slightly more stable (9.6 kJ/mol), but the conjugated diene must be s-cis conformation for the Diels-Alder reaction to occur.
The End Rule
In general, endo is the major product.
- The transition state is formed when the dienophile are pointing towards the π electrons of the diene.
- The increased rate of endo product formation is due to interaction between the π electrons of the substituent and the π electrons of the ring, which stabilizes the transition state.
