DielsAlder and other pericyclic reactions

1
Diels-Alder and other pericyclic reactions
Part 3
2
Homework

• Read 27.5A-E, and handout (sections 1.5-1.10 from
  Benoiton)
• Answer questions 27.41,43,44, 48,49,50

3
Aromatic Transition States - The Frontier-Orbital
Method

• Cycloaddition reactions are allowed only when all
  overlaps between the HOMO of one reactant and the
  LUMO of the other are such that a positive lobe
  overlaps only with another positive lobe and a
  negative lobe, only with another negative lobe

Anti-bonding
Bonding
Dienophile
Diene
4
Aromatic Transition States - The Frontier-Orbital
Method

• Cycloaddition reactions are allowed only when all
  overlaps between the HOMO of one reactant and the
  LUMO of the other are such that a positive lobe
  overlaps only with another positive lobe and a
  negative lobe, only with another negative lobe

Anti-bonding
Bonding
Dienophile
Diene
5
Aromatic Transition States - The Frontier-Orbital
Method
Why do 4n2 reactions happen and 4n do not?
HOMO
LUMO
6
Aromatic Transition States

• decarboxylation of ?-keto acids and
  ?-dicarboxylic acids (Section 17.9)

H
H
O
O
O
O
O

C
O
O
7
Aromatic Transition States

• the Diels-Alder reaction
• pyrolysis of esters (Problem 22.42)
• two more pericyclic reactions (reactions that
  proceed by aromatic transition states)
• Claisen rearrangement
• Cope rearrangement

Adduct
Diene
8
Great chemists
Ludwig Claisen, 1851-1930 Aachen (1890), Kiel
(1897), Berlin (1904)
Arthur Clay Cope, 1909-1966 Massachusetts
Institute of Technology

• Condensation of esters
• Rearrangement of allyl phenols
• Glassware apparatus

• Elimination of quaternary ammonium oxides
• Rearrangement of 1,5-dienes

9
Claisen Rearrangement

• Claisen rearrangement a thermal rearrangement of
  allyl phenyl ethers to 2-allylphenols

O
10
Claisen Rearrangement
O
11
Claisen Rearrangement
Microwave-Mediated Claisen Rearrangement Followed
by Phenol Oxidation A Simple Route to Naturally
Occurring 1,4-Benzoquinones. The First Syntheses
of Verapliquinones A and B and Panicein
A Christopher J. Davis, Timothy E. Hurst,
Aouregan M. Jacob, and Christopher J. Moody J.
Org. Chem. 2005 70(11) pp 4414 - 4422
12
Cope Rearrangement

• Cope rearrangement a thermal isomerization of
  1,5-dienes

13
Cope Rearrangement

• Predict the product of these Cope rearrangements

(a)
14
Carbon-Carbon Bond Formation and Synthesis
End Chapter 24