1. EPOXIDE FORMATION AND CLEAVAGE

2. EPOXIDE Epoxides are cyclic ethers Three-membered ring compound Also known as oxiranes

3. Epoxidation Epoxidation is an electrophilic addition Involves NGP Preparation: Peroxy oxidation of alkenes Base promoted cyclization of vicinal halohydrins

4. Epoxidation: Syn addition Oxidation of Alkene Most widely used method Reaction of an alkene with an organic peroxy acid (peracid).

8. C O bonds in the epoxide are not perfectly axial or equitorial Requirement Diaxial and trans position of leaving groups Epoxidation –single step process & stereospecific. Doesn’t involve a free carbocation. (i.e) Reactant Product Cis Cis Trans Trans

9. Axial Equitorial Pseudo axial Pseudo equitorial Axial Equitorial Pseudo axial Pseudo equitorial

11. Ring Opening Ring opening due to ring strain Regioselectivity of opening depend on condition Acid Catalysis Acid catalysis Nu - attack more substituted carbon atom (if unsymmetrical)

12. Ex: acid catalysis B is the major product

14. Base Catalysis Base catalysis Nu - attack less substituted carbon atom Ex:

16. Conclusion Epoxides unlike ethers are reactive because of ring strain Most often used peoxy acids for epoxidation MCPBA (Meta chloroperoxy benzoic acid) MMPP (Magnesium monoperoxyphthalate)

17. Transition state is similar for both formation and cleavage

18. Reference Organic Chemistry (Clayden, Greevs, Warren,Wothers) Fundamentals of Organic Chemistry (Solomons & Graham) Stereochemistry Conformation and Mechanism ( P.S.Kalsi)