The reaction of sulfur ylides with carbonyl compounds such as ketones or the related imines leads to the corresponding epoxides or aziridines.
The reaction of sulfur ylides with enones gives cyclopropanes.
Mechanism of the Corey-Chaykovsky Reaction
The ylides are generated in situ by the deprotonation of sulfonium halides with strong bases.
Dimethyloxosulfonium methylide - known as the Corey-Chaykovsky Reagent - is a valuable alternative to dimethylsulfonium methylide and can be generated from trimethylsulfoxonium iodide.
Higher substituted ylides can be generated selectively if one substituent is preferably deprotonated over the others, for example when the negative charge is stabilized or the environment is sterically less demanding:
Such ylides are able to transfer more than just a methylene group, and enantioselective induction can be observed if the ylide is chiral:
The ylide initially acts as a nucleophile toward the carbonyl compound. The resulting oxygen anion then reacts as an intramolecular nucleophile toward the now electrophilic ylide carbon, which bears a sulfonium cation as a good leaving group:
The reaction of the Corey-Chaykovsky Reagent with enones is a 1,4-addition that is followed by ring closure to give a cyclopropane:
As sulfides are readily alkylated, it is even possible to use them catalytically. Such methods can give very interesting results when expensive chiral sulfides are used for the generation of chiral epoxides.
For a review of enantioselective methods see: V. K. Aggarwal, J. Richardson, Chem. Commun. 2003, 2644. DOI
With phosphorus ylides as used for the Wittig Reaction, the phosphorus atom forms a strong double bond with oxygen. This leads the mechanism in a different direction, to effect olefination instead of epoxidation through intermediate oxaphosphetanes.
Design of Sulfides with a Locked Conformation as Promoters of Catalytic and Asymmetric Sulfonium Ylide Epoxidation
M. Davoust, J.-F. Briere, P.-A. Jaffres, P. Metzner, J. Org. Chem., 2005, 70, 4166-4169.
Catalytic Asymmetric Synthesis of 2,2-Disubstituted Terminal Epoxides via Dimethyloxosulfonium Methylide Addition to Ketones
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B. S. Kumar, V. Venkataramasubramanian, A. Sudalai, Org. Lett., 2012, 14, 2468-2471.