Diels alder reaction is activated by photochemical reaction.it plays a vital role in drug discovery and synthesis.

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Why?
Diels –Alder reaction is
important…!

3. Do You Know?
 Otto Diels and his research student
Kurt Alder worked at the university
of kiel and discovered this
reaction in 1928.
 They won Nobel prize in 1950.
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4. CONTENTS
Diels – Alder reaction
Stereochemistry in D-A reaction
Endo rule in D-A reaction
Solvent in D-A reaction
Intramolecular D-A reaction
Regioselectivity in D-A reaction
Lewis acid in D-A reaction
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5. Diels – Alder Reaction
[4+2] cycloaddition
Two unsaturated molecule undergo
addition reaction through cyclic transition
state to form a product.
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6. What is diene?
Two double bonds must be in conjugated.
What is dienophile?
Alkene with #EWG
# Extra Conjugation
# phenyl group
O
O
O
CHO O2N
O
O 6

7.  Diels – Alder reaction occur between a
conjugated diene and alkene (dienophile)
[ 4 + 2 ]
 Transition state has six delocalized pi-
electrons, thus aromatic In character.
+
O
O
O
Heat
O
O
O
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8. Diene must have the S-Cis
conformation.
Alkene also act as
 dienphile, but it shows
 poor reaction.
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9. Stereochemistry
 Diels – Alder reaction is stereospecific
In Dienophile:
 If there is stereochemistry in dienophile,
then it is faithfully reproduced in the
product.
e. g.,
 Esters of maleic and fumaric acid in
Diels – Alder reaction. 9

10. In Diene:
Diene also influence the stereochemistry of the product.
1) cis,cis
2) Trans ,trans
3) Cis,trans
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12. Endo rule for D-A reaction
 If both reactants are cyclic ,then the
product must be Endo product.
 If the both reactants are cis
conformations, it prefers selectively
Endo product only.
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13. Exo product is more stable than endo product(steric
hindrance),though Endo product is preferred in D-A
reaction.
Endo forms faster because, there is some interaction
b/w newly formed double bond and other end
carbonyl group.
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14. Solvent in D-A reaction
 D-A is solvent free (pericyclic)
reaction.
 The reaction can undergo with
solvent.
 Organic solvent are the best for this
reaction.
 But, adding some water into the
solvent increase the yield and
selectivity.
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15. Intramolecular D-A reaction
 Generally, intramolecular reaction
prefers exo product.
 Intramolecular D-A reaction are
goverend more by normal steric than
endo rule.
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16. If there is carbonyl group present in
conjugate to the dienophile, leads to
endo product.
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17. Regioselectivity in D-A reaction
Regioselectivity is consider only when
the diene have substitution.
If its electron donating group (Me, OR,
Me3SiO, NR2, NH2, etc…)
Substituted at the end give Ortho
product.
Substituted at the middle gives Para
product.
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18.  In presence of lewis acid catalyst, the
regioselectivity is increased respectively,
 This is due to lewis acid coordinate with
carbonyl compound,
Lewis acid in D-A reaction
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19. Summary
 D-A reaction undergo through [4+2]
cycloaddition.
 Diene and dienophile is important in
reaction.
 D-A reaction is stereospecific.
 D-A reaction prefers Endo product
 Intra D-A reaction prefers Exo product.
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20.  Water mixture solvent increase the
yield and selectivity.
 Regioselectivity in D-A reaction
prefers Para substituted product.
 Lewis acid – para product is
increased.
Reference
Book: organic chemistry by Clayden
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21. Synthetic importance of D-A
reaction in drug synthesis
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22. Thank you
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