Review Of Organic Chemistry Page 22

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Organic Chemistry I Review: Highlights of Key Reactions, Mechanisms, and Principles
22
A. The General Diels-Alder Reaction
1
1
W
W
2
2
heat
6
6
3
5
3
5
4
4
dienophile
diene
1. Electronics: The diene HOMO reacts with the dienophile LUMO
 Effectively the diene is the nucleophile and the dienophile functions as the electrophile
2. The dienophile usually needs an electron-withdrawing attachment (“W”) (at least one)
 This makes the dienophile more electrophilic
 Electron Withdrawing Groups to Memorize:
Carbonyls
Others
CF
SO
H
CN
NO
!-
!-
3
!-
!-
3
2
O
!-
O
!-
O
O
O
F
O
!+ !-
!+
!-
C
!+
C
C
C
OR
NH
S
OH
C F
H
R
C N
2
N
!+
!+
!+
!+
O
!-
!-
O
F
 Keys:
 The atom that is connected to the alkene has δ+ charge
 Anything with a double-bond to a heteroatom tends to have this
o C=O, C≡N, N=O, S=O
B. Predicting Products When the Diene or the Dienophile (or both) is Symmetric
1. Always make a cyclohexene 6-ring product
2. Number the diene from 1-4, and identify those four carbons in the product ring.
3. A double bond in the product will always exist between carbons 2 and 3.
4. Any substituents on the diene or dienophile are spectators: they will be attached to the same
carbons at the end.
• Beware of cyclic dienes
• Beware of dienes that are drawn in their zigzag s-trans form, but could react following
rotation into an s-cis form
C. Stereochemistry: For Cis- or Trans- Disubstituted Dienophiles
• Both carbons of a disubstituted dienophile usually turn into stereocenters.
1. Cis in  cis out: If two substituents on the dienophile are cis to begin with, they will still have
a cis relationship on the product cyclohexene
2. Trans in  trans out: If two substituents on the dienophile are cis to begin with, they will
still have a cis relationship on the product cyclohexene
• Note: this is for the dienophile only. The diene alkenes may also have substitution such that
one or both diene double bonds are cis or trans, but the “cis-in-cis-out” guideline does not apply
to the diene.

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