Cycloaddition reactions

Cycloaddition reactions: combination of two words "cyclo" and "addition", which means addition of two molecules to form a new ring system.
Reterocycloaddition reactions : reverse of cycloaddition reactions is known as reterocycloaddition reactions
Types of cycloaddition reactions
Mechanism of cycloaddition reactions
Suprafacial and antarafacial interactions
Woodward-Hoffmann rule for cycloaddition reactions
Examples and applications of cycloaddition reactions

1. Cycloaddition Reactions Presented By: ABU BAKAR 18551507-078 BS Chemistry VI-B Supervisor: Dr. Ghulam Mustafa CHEM-311 (Organic Chemistry-III)

2. Synopsis Introduction Retrocycloaddition Classifications Mechanism Suprafacial and Antarafacial Interactions Woodward-Hoffmann Rules for Cycloaddition Reactions Examples Applications References

3. Introduction Cycloaddition (cyclo = ring) reactions involve the combination of two molecules to form a new ring. In cycloaddition reactions, two unsaturated molecules or two unsaturated parts of a single molecule undergoes an addition reaction. 2 π -bonds breaks and 2 new σ -bonds are formed (∆ σ = 2).

4. Retro-cycloaddition Cycloaddition reactions are reversible, and it is possible to carry out the reverse reaction by a suitable choice of substrates and reaction conditions. The reverse cycloaddition is called retro-cycloaddition or cycloreversion. Retro-cycloaddition is unimolecular and commonly, ∆ σ = -2. Cycloaddition Retro-cycloaddition 2 π -bonds breaks 2 π -bonds formed 2 σ-bonds formed (∆σ = 2). 2 σ-bonds breaks (∆σ = -2). Bimolecular Unimolecular

5. Types of Cycloaddition Reactions There are many types of cycloaddition reactions depending upon the number of π -electrons involved. If the number of π -electrons in the reacting components are m and n respectively, the cycloaddition reaction is called [m+n] cycloaddition.

6. Mechanism of Cycloaddition Reactions A cycloaddition mechanism is characterized by concerted bond-breaking and bond-forming processes with cyclic movement of electrons in a single transition structure (TS). Concerted implies that bond-breaking and bond-forming events are simultaneous (at the same time).

7. Suprafacial and Antarafacial Interaction Bonding interaction between the lobes on the same face of the one reactant and lobes on the same face of the other. Bonding interaction between the lobes on the same face of the one reactant and lobes on the opposite face of the other.

8. Woodward-Hoffmann rules for [2+2] Cycloaddition Reactions

9. Woodward-Hoffmann rules for [4+2] Cycloaddition Reactions

10. Woodward-Hoffmann rules for [4+2] Cycloaddition Reactions

11. Woodward-Hoffmann Rule for Cycloaddition Reactions Sum of the number of π -electrons of both the reactants taking part in reaction Reaction Conditions Allowed mode of Bond Formation 4n (4,8,12, etc.) Thermal Antarafacial Photochemical Suprafacial 4n + 2 (6,10,14 etc.) Thermal Suprafacial Photochemical Antarafacial

12. Examples of Cycloaddition Reactions

13. Applications of Cycloaddition Reactions Cycloaddition reactions are certainly the most important and powerful tools for the construction of cyclic molecular architectures. These reactions rapidly increase molecular complexity and the products are often formed with high stereoselectivity and a high degree of functionality. These reactions are useful for the synthesis of natural products, pharmaceutical agents, and other materials from relatively simple starting materials. The [4+3] cycloaddition reaction leads directly to seven-membered rings, and there are a myriad of natural products that possess impressive and diverse biological activity that is of interest to both human and animal health that contain this medium-sized ring.

14. Applications of Cycloaddition Reactions Cycloaddition reactions are used in the synthesis of Tropane Alkaloids, monotropenoids and lactone. The Diels-Alder reaction is used in the production of Vitamin B6. The research group of Andrew G. Myers of Harvard University developed a platform for the synthesis of a diverse range of tetracycline antibiotics which relies on the Diels-Alder reaction.

15. References PERICYCLIC CHEMISTRY Orbital Mechanisms and Stereochemistry by Dipak K. Mandal. (Page # 63-65, 69-70, 111-152) ORGANIC MECHANISMS Reactions, Methodology, and Biological applications by Xiaoping Sun. (Page # 131-135) ADVANCED ORGANIC CHEMISTRY Part A: Structure and Mechanisms by Francis A. Carey and Richard J. Sundbery (Fifth edition). (Page # 834-838) METHODS AND APPLICATIONS OF CYCLOADDITION REACTIONS IN ORGANIC SYNTHESES by Nagatoshi Nishiwaki. (Page # 599-627)

16. References ORGANIC CHEMISTRY by Jonathan Clayden, Nick Greeves, and Stuart Warren (Second Edition). (Page # 877-908) Sana Ullah’s Advanced Organic Chemistry (Mechanistic Approach). (Page # 713-729) Haq Nawaz Bhatti Advanced Organic Chemistry. (Page # 489-498)