Johnson-Corey-Chaykovsky reaction

The Johnson-Corey-Chaykovsky reaction is a chemical reaction in which a carbonyl is converted to an epoxide by the action of a sulfonium ylide. The reaction can be viewed as a methylene transfer.



The original publication by Johnson in 1961 concerned the reaction of 9-dimethylsulfonium fluorenylide with benzaldehyde. The attempted Wittig reaction failed and a benzalfluorene oxide was obtained instead.



Variations


Dimethyloxosulfonium methylide, (CH3)2SOCH2, is known as the Corey-Chaykovsky reagent, or CCR for short. CCR is a sulfoxide-ylide and used as a methylene-transfer reagent. Since it is stable for only short periods, it is typically generated in situ.

Trimethyl sulfoxonium iodide, obtained by reaction of DMSO and methyl iodide, can be reacted with a strong base such as sodium hydride to generate the Corey-Chaykovsky reagent. An alternative procedure for in situ ylide formation is by reaction of trimethylsulfonium iodide, Me3SO+I-, and NaHMDS. CCR was first demonstrated with benzophenone as a substrate.



The reaction mechanism for this reaction type consists of nucleophilic addition of the ylide to the carbonyl group. A negative charge is transferred to the oxygen carbonyl anion and because the sulfonium cation is a good leaving group it gets expelled forming the oxirane. In the related Wittig reaction, the formation of the much stronger phosphorus oxygen double bond prevents oxirane formation and instead olefination takes place through a 4-membered cyclic intermediate.