This document summarizes different types of cycloaddition reactions. It begins by defining cycloaddition reactions as those where two unsaturated molecules react to form a cyclic product through the loss of two pi bonds and gain of two sigma bonds. It then classifies cycloaddition reactions based on the number of pi electrons involved - [2+2], [4+2], and 1,3-dipolar cycloadditions. Examples of each type are provided along with diagrams to illustrate the reaction mechanisms and orbital interactions. Applications of cycloadditions in organic synthesis are also briefly mentioned.

1. SAMARAT PRITHVIRAJ CHAUHAN
GOVERNMENT COLLAGE,AJMER
2021-22
DEPARTMENT OF CHEMISTRY
CYCLOADDITION REACTIONS
Submitted BY:
Manisha kanwar
M.Sc(Chemistry) Semester 2nd

2. CONTENTS
• Cycloaddition reaction.
• Facts of cycloaddition reaction.
• Terminology- supra-antra mode
Symmetry
• F.M.O method.
• [ 2+2 ] cycloaddition reaction.
• [4+2 ] cycloaddition reaction.
• 1,3 dipolar cycloaddition reaction.
• Application of cycloadditions.
• Reference

3. CYCLOADDITION REACTIONS
 A cycloaddition is a reaction in which two unsaturated molecules
undergo an addition reaction to yield a cyclic product . Formation
of cyclic product takes place at the expence of one П bond in
each of the reacting partner and gain of two sigma bonds at the
end of the both components having pi bonds. Thus in this
reaction there is loss of two pi bonds of the reactants and gain of
two sigma bonds in the product.

4. THE CYCLOADDITION REACTION ARE CLASSIFIED
WITH RESPECT TO THREE FACTS OF THE REACTION :
 (i) A cycloaddition reaction involves the formation of two 
bonds between the termini of two independent -systems,
resulting in ring formation - or the reverse process.
 (ii) Cycloaddition reactions are stereospecific (e.g. cis/trans
isomers). The stereospecificity being afforded by the suprafacial
or antarafacial nature of the approach of the two -units in the
transition state.
 (iii) The suprafacial or antarafacial process involved in the 
bond making process is controlled by the HOMO/LUMO
interactions of the two -systems in the transition state.

5. • New bonds to the same
side of the -system
• New bonds to the
opposite side of the -
system

6. SYMMETRY IN LINEAR CONJUGATED PI-
SYSTEM
M-Symmetry(mirror-symmetry)
• M-symmetry means plane
of symmetry
C2-Symmetry(centre-symmetry)
• C2-symmetry means centre
of symmetry

7. FMO METHOD
 In order for a cycloaddition to occur,must be bonding overlap
between p orbital at the terminal carbons of each  electron system
,this is where the new sigma-bonds are formed. Lets us explain this
point with a [4+2] cycloaddition. Let us suppose that diene (4-
component) behaves as electron donar and the dienophile (2-
component)as the electron acceptor.

8. [2+2] CYCLOADDITION
REACTION
 When 2 electron and 2 electron system
combine together to give cycloalkene the reaction
is called 2+2 cycloaddition it can occur suprafical
antrafacial mode of addition.

9. [2+2] CYCLOADDITIONS
 THERMAL INDUCED

10. [2+2] CYCLOADDITIONS
• PHOTO INDUCED-

11. [4+2] CYCLOADDITION REACTION
• A cycloaddition reaction is the concerted bonding together of
two independent pi-electron systems to form a new ring of
atoms. ... The Diels-Alder cycloaddition is classified as a [4+2]
process because the diene has four pi-electrons that shift
position in the reaction and the dienophile has two.

12. [4+2] cycloaddition reaction
• THERMAL INDUCED REACTION –There are two
possible interactions, HOMO (diene) – LUMO
(dienophile) and HOMO(Dienophile)-LUMO(diene).
• 1.HOMO(Diene)-LUMO(dienophile)

13. • 2….HOMO(Dienophile)-LUMO (Diene)

14. [4+2] cycloaddition reaction
• PHOTO INDUCED REACTION-When diene is excited
by light.its HOMO becomes Ψ₃* which has m
symmetry and this MO cannot overlap with LUMO
of ethylene which has C₂ symmetry.
• Thus photochemical
Cycloaddition of [4+2]
Systemis symmetry
forbidden reaction.

15. 1,3 –DIPOLAR CYCLOADDITIONS
• 1,3-Dipolar cycloadditions represent synthetically important
reactions for the preparation of heterocyclic five-membered
rings. They belong into the group of [4+2] cycloadditions
according to the Woodward-Hoffmann classification.
•

16. • INTERACTION BETWEEN HOMO OF 1,3-DIPOLE
AND LUMO OF DIPOLARPHILE

17. APPLICATIONS OF CYCLOADDITIONS
• N1 unit transfer reaction to C–C double bonds.
• [3+2] Cycloaddition of α, β-unsaturated metal-carbene
complexes.
• Formal [3+3] cycloaddition approach to natural product
synthesis.
• Development of new methods for the construction of
heterocycles based on cycloaddition reaction of 1,3-
dipoles.
• Cycloreversion approach for preparation of large π-
conjugated compounds.
• Transition metal-catalyzed or mediated [5+1]
cycloadditions.
https://www.wiley.com/en-
us/Methods+and+Applications+of+Cycloaddition+Reactions+in+Organic+Syntheses-p-9781118299883

18. REFERENCE
• Advance organic chemistry- DR. JAGDAMBA
SINGH(Pragati edition).
https://www.goodreads.com/work/editions/66293573-advance-organic-chemistry
• Cycloaddition reaction in organic synthesis-
W.Carruthers.
Print ISBN:9783527301591 |Online ISBN:9783527600250
|DOI:10.1002/3527600256