Diels – Alder Reaction
1,4-CycloAddition Reaction of Dienes
Solomons and Fryhle: 13.11
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What is a Diels-Alder 1,4 Cycloaddition Reaction?
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What’s Going With Respect to a Diels-Alder 1,4 Cycloaddition Reaction?
Diene
Dieneophile
Diels Alder Adduct
X
+
S-cis
X
Cyclohexene derivative
3 π bonds convert into one π bond + two σ bonds
Note: σ bond stronger > π
Note: No formal charge formed, hence solvents polarity is not that important
3
Examples of Dienes and Dienophiles
Prefer electron withdrawing groups on dienophile
Prefer electron donating groups on diene
4
Examples of Dienes and Dienophiles
200o C
+
20% yield
O
+
H
O
30o C
H
100% yield
OR>> Employ electron withdrawing groups on dienes and electron donating
groups on dienophile
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Diels Alder Reaction is VERY Stereospecific!!
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H
Endo
H
H
H
CO2CH3
H
H
H
H
Exo
H
CO2CH3
H
Nomenclature
7
Diels Alder Stereochemistry
Exo Product is usually thermodynamic product but formed slowly
Endo Product is the kinetic product and frequently predominates
8
Diels Alder Stereochemistry
Endo and exo addition require different approach and transition state geometries
Endo
Exo
Better secondary overlap of π orbitals for endo>> Kinetic Product
9
Problem from Solomons and Fryhle 13.24 b and f: What diene and dienophile would
you employ in a synthesis of the following?
O
Me
O
Me
O
O
Me
H
Me
OCH3
O
10
Problem provide a synthetic path for the following:
Starting Material
>>>>>>>>>>>>>>>
Product
O
11
For “fun/practice” look at
S&F 13,16, 18, 19, 24, 25, 28, 40
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Now for Something New
Chapter 14
Aromatic Compounds and Chemistry
Solomons and Fryhle: 14.1,2,3,10
13
No reaction
Very Slow and requires high
Pressure
14
R
Solomons and Fryhle, problem 14.16,17
15
ortho
meta
para
16
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