conjugated systems diels alder...
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Conjugated SystemsDiels Alder Reactions
Dr. Sapna Gupta
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Diels-Alder Reaction
• Otto Diels, Kurt Alder; Nobel prize, 1950
• Conjugate dienes can combine with alkenes to form six-membered cyclic compounds
• The formation of the ring involves no intermediate (concerted formation of two bonds)
• Diene + dienophile will give an adduct/product
Conjugated System 2
adduct
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Examples of Diels-Alder Reactions
Conjugated System 3
No ring in diene or dienophile:One cyclohexene ring in product.
One ring in diene:One cyclohexene ring in product + one more ringBicyclic product.
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Mechanism - Concerted
There is no clear nucleophile or electrophile.
Conjugated System 4
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Dienes and Dienophiles
Conjugated System 5
Diene Dienophile
• The diene component.• Is more effective when it is
electron rich.• It can be made more electron
rich by adding more electron donating groups.
• The alkene component.• Is more effective if it electron
poor.• It can be made more electron
poor by adding groups that are electron withdrawing.
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Groups on Dienes and Dienophile
Conjugated System 6
For Dienes For Dienophiles Some effective Dienophiles
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Stereospecificity in Diels-Alder Reaction
Conjugated System 7
Trans dienophilegive a trans product
Cis dienophilegive a cisproduct
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Regioselectivity of Diels-Alder Reaction
Reactants align to produce endo (rather than exo) product. Endo and exoindicate relative stereochemistry in bicyclic structures.
Conjugated System 8
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Conformation of the Diene
• The relative positions of the two double bonds in the dieneare “cis” or “trans” to each other about the single bond (being in a plane maximizes overlap)
• These conformations are called s-cis and s-trans (“s” stands for “single bond”)
• Dienes react in the s-cis conformation in the Diels-Alder reaction
Conjugated System 9
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Key Concepts
• Diene – Dienophile
• Electron withdrawing and donating groups.
• Stereoselectivity
• Regioselectivity
• Conformation of the diene
Conjugated System 10