Corey-Chaykovsky Reactions
The Corey-Chaykovsky reactions allow the preparation of epoxides from aldehydes or ketones and aziridines from imines using sulfur ylides. Also, alpha,beta-unsaturated carbonyl compounds produce cyclopropane derivatives.
General features:
1. The reaction is most often employed for epoxidation via methylene transfer. 2. Sulfur ylides are more reactive and less stable than sulfoxonium ylides, so they are generated and used at low temperatures. 3. The reaction of substituted sulfur ylides with aldehydes is stereoselective, leading to trans epoxides.
Corey-Chaykovsky Reactions
Reaction Mechanism
Epoxidation: 1. Formation of the sulfonium ylide. 2. Nucleophilic addition of the ylide to the carbonyl carbon. 3. Oxirane formation.
Cyclopropanation: 1. Formation of the sulfoxonium ylide. 2. Conjugate addition of the ylide to the enone. 3. Cyclopropane formation.
Example
Experimental Procedure
Trimethylsulfonium iodide (1.65 eq) was added to dry DMSO (25 mL) and stirred until complete dissolution of the salt. Addition of the allyl cyclohexanone (7.15 mmol, 1.0 eq), followed by addition of a solution of potassium tert-butoxide (1.65 eq) in DMSO (17 mL). The resulting solution was kept under stirring at room temperature for 2 hours. After this time, H2O was added, and the reaction mixture was extracted with ethyl ether. The organic phase was washed with H2O, dried over anhydrous MgSO4, and the solvent evaporated. The crude was purified by column chromatography to afford the desired epoxide (88% yield).
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