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1. M.S.C Semester -1
EXAMINATION -2019
PROJECT NOTEBOOK
ON
PERICYCLE REACTION
(DIELS-ALDER REACTION)
SUBMITTED BY
NAME :- KASTURI MANDAL
UID NO :- 19003014012
REG NO :- 00026 OF 2019-2020
N

2. CONTENTS
1.Pericycle Reaction
2.Sigmatropic Reaction
3.Cycloadditions Reaction
4.ElectroCyclic Reaction
5.Cheletropic Reaction
6.Diels-Alder Reaction
7.Chapter I
8.FMO Approach
9.Chapter II
10.Endo-addition
11.Exo-addition
12.Regio Selectivity
13.Chapter III
14.Application
15.Conclusion

3. Pericyclic Reaction
• Scientist Woodward and Hoffmann have suggested the term
‘Pericyclic Reactions’(it means around the circle) for those
reactions where :
a. Reactant-bonds are broken and product-bonds are formed simultaneously by way of a
single transition state
b. Involve electrons shift in cyclic manner
Classifications :
There are four types of pericyclic reaction
a) Sigmatropic Reaction
b) Cycloadditions Recation
c) ElectroCyclic Reaction
d) Cheletropic Rection

4. Sigmatropic Reaction
Sigmatropic reaction is defined by the migration of a σ –bond(sigma bond)
adjacent to one or more ∏-systems, with the ∏-systems becoming reorganized in
the process. In the reaction the total number of σ or ∏ bonds does not change as
the reactant and the product have the same number of bonds.

5. Cycloaddition Reaction
Cycloaddition reactions involve concerted combination of two ∏-elctron
systems to form a ring system. Among the Pericyclic reactions , cycloadditions
are most useful and abundant set of reactions.

6. Elctrocyclic Reaction
Electrocyclic reactions are characterized by the creation of ring from an open
chain conjugated system , with a σ –bond(sigma bond) forming across the end
of the conjugated system on opening of a cyclic system under ring strain to give
rise to a diene.

7. Cheletropic Reaction
Cheletropic reaction is one type cycloaddition reaction in which one of the
reacting species or fragments acts through a single atom possessing both a
filled and an empty orbital .

8. Diels-Alder Reactions
Introduction :
• Diels-Alder reaction is a reversible cycloaddition reaction where diene with 4∏ electrons reacts
with a 2∏ electron dienophile , suprafacially on each component to from a six membered cyclic
system .
• It is (4∏+ 2∏) electron reaction .
• Diels-Alder reaction was first described by two German chemist Otto Paul Hermann Diels and Kurt
Alder in 1928
• They were awarded the Nobel Prize in chemistry in 1950
• The work by Diels and Alder is described in a series of 28 articles published in the Justus Liebigs
Annalen der Chemie and Berichte der deutschen chemischen Gesellschaft from 1928 to 1937.

9. Chapter I
Theory :
• For the best known [4+2] cycloaddition is the Diels-Alder reaction,in which a conjugated diene(4∏
system) on heating with dienophile(4∏ system) forms a six membered ring .
• This is also called 1,4 cycloaddition reaction .

10. Chapter I…..Contd
• The reaction is reversible and reverse path is known as retro Diles-
Alder reaction ,which is favored at high temperature .
• Dienes in Diels-Alder reaction must be in cisoid conformation
• This is essential for the formation of six membered cyclic transition
state for the reaction .
Example :
1,3-Butadiene though sterically more stable in it’s transoid
conformation ,it reacts with a dienophile after being cisoid by rotation
against c-c σ –bond .

11. Chapter I…..Contd
So, cyclic dienes with permanent cisoid structure are therefore very
good for Diels-Alder reaction while Diene with rigid transoid are
unreactive

12. FMO Approach
Dienophile Diene
Ѱ2
Ѱ1
Ѱ4*
Ѱ3*
Ѱ2
Ѱ1
Π *
Π *

13. FMO Approach…contd
HOMO of
Diene (Ѱ2)
LUMO of
Dienophile
Ѱ(2*)
HOMO of
Dienophile
(Ѱ1)
LUMO of
Diene (Ѱ3*)
+ +

14. Chapter II
• When both the diene and dienophile are substituted then the
stereochemical relationship of these substituents my have two
possibilities .
Types :
a) Endo-addition
b) Exo-addition

15. Endo-addition
• Endo transition state and adduct is more sterically congested thus thermodynamically less stable .
• But it is normally the predominant product .
• Endo products are kinetically controlled product .
Cyclopentadiene
maleic anhydride endo adduct

16. Exo-addition
• Exo-addition leads to the formation of an isomeric product in which substituents on the dienophile project
away from the Diene .
• Exo-products are thermodynamically controlled product .
• In Exo-addition, the dienophile is flipped relative to the diene and the addition occurs to the opposite face of
the dienophile.

17. Regioselectivity
• Even when both the diene and dienophile are both unsymmetrically substituted , the Diels-Alder
product is usually a single isomer rather than a mixture .
a) When electron-donating group is present on the middle carbon of the diene.

18. Regioselectivity….Contd
b) When electron-donating group is present on the terminal carbon of the diene.

19. Stereochemistry of the adduct due to
stereochemistry of the dienophile
• The Diels-Alder reaction is
stereospecific .
• Substituents that are cis in
the dienophile remain cis
in the product and
substituents that are trans
in the dienophile remain
trans in the product .

20. Stereochemistry of the product due to the
stereochemistry in the diene

21. Chapter III
• The Diels-Alder reactions proceed under mild conditions , give high yields and form only
inoffensive by products ,do not require any metal catalyst .
• Preparation of pentane-1,2,4-tricarboxylic acid .

22. Chapter III…..Contd
• Pentane-1;2,4-tricarboxylic acid is a multifunctional compound and the first step is Diels-Alder
reaction to prepare this.
• With this compound derivative we may prepare very useful drug molecules and other types of
important organic small molecules by functional group interconversion .
• Prostaglandin is a hormone-like substance that substance that participate in a wide range of body
functions such as the contraction and relaxation of smooth muscle, control of blood pressure ,
modulation of inflammation etc.
• During the preparation of the prostaglandin Diels-Alder reaction is the first step .

23. Application
• The first application of Diels-Alder reaction in total synthesis was illustrated by R.B. Woodward’s
synthesis of the steroids cortisone and cholesterol .
• A simple and effective Diels-Alder reaction can be employed in the preparation of linear
thermoplastic & thermosetting polymers such as polyimides, polyphenylens , ladder polymer etc.
• Diels-Alder reaction employed in the production of vitamin B6,B12 .
• The retro Diels-Alder is used in the industrial production of cyclopentadiene which is precursor to
various norbornenes , which are common monomers .

24. FUTURE RESEARCH

25. FUTURE RESEARCH….COND

26. Conclusion
• Diels-Alder reaction is a very significant reaction .
• It is a very cheap reaction and percentage of yield is very high .
• So it is a very profitable reaction for industry purpose .
• It is easy to do this chemical reaction than other organic chemical
reaction as the procedure of this reaction is very simple .