Review Of Organic Chemistry Page 21
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34Organic Chemistry I Review: Highlights of Key Reactions, Mechanisms, and Principles
21
Section 15.11 The Diels-Alder Reaction. The Reaction of Conjugated Dienes (Dienes) with
Electron-Poor Alkenes (Dienophiles) to make Cyclohexenes.
Quick Overview Summary
1
1
2
6
6
2
heat
1.
3
5
3
5
4
4
dienophile
diene
2. s-cis diene conformational requirement: The diene must be locked or be able to single-bond
rotate it’s way into the “s-cis” conformation in order to react
1
1
"cisoid" or "s-cis"
2
2
"transoid" or "s-trans"
-meaning that it's "cis" relative
-relative to the single bond
3
to the single bond
3
-even though the single bond
4
4
is capable of rotation
can't
can
react
react
3. Rate Factors
1. Dienophile
activated by electron withdrawing groups (“W” or “EWG”) for electronic reasons
2. Diene:
Deactivated by substituents that make it harder or less stable to exist in the s-cis
conformation. This is true when a diene alkene has a Z-substituent.
Steric factors equal, activated somewhat by electron donating groups (“D” or “EDG”)
4. Concerted Mechanism
1
1
All bond making and breaking happens at once:
6
*3 !-bonds break
heat
6
2
2
*2 "-bonds and 1!-bond form
5
3
4
5
3
4
The diene is really the "nucleophile" (HOMO)
The dienophile is really the "electrophile" (LUMO)
5. Orbital Picture
6. Product Prediction Highlights
Try to match up the 4 diene and 2 dienophile carbons with the product
o The product double bond will be between C2 and C3 of the diene
Substituents are spectators
1,4/1,2 Rule: when asymmetric dienes react with asymmetric dienophiles
o Match δ- end of nucleophilic diene with δ+ end of electrophilic dienophile
For disubstituted dienophiles:
o cis-substituents end up cis, and trans-substituents end up trans
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