Corey-Chaykovsky epoxidation

What is Corey-Chaykovsky epoxidation?

The Corey-Chaykovsky reaction, which enables the preparation of monosubstituted or geminally disubstituted epoxides from aldehydes or ketones using methylsulfonium or methyloxosulfonium ylides, was first reported by Johnson in 1958 but was later explored extensively by Corey and Chaykovsky in the 1960s. This reaction is also known as Corey-Chaykovsky epoxide synthesis, Corey-Chaykovsky epoxidation, or Corey-Chaykovsky oxiranylation.

Corey-Chaykovsky epoxidation - general reaction scheme - Corey-Chaykovsky epoxide synthesis - Corey-Chaykovsky oxiranylation
Corey-Chaykovsky epoxidation
Corey-Chaykovsky epoxidation - general reaction scheme - Corey-Chaykovsky epoxide synthesis - Corey-Chaykovsky oxiranylation
Corey-Chaykovsky epoxidation

The Corey-Chaykovsky reagent refers to either methylsulfonium or methyloxosulfonium ylide. Trimethylsulfoxonium ylide Me2S=CH2 is traditionally prepared from trimethyl sulfoxonium iodide with NaH in DMSO, and it is stable at 0 °C in an inert atmosphere. It reacts with carbonyl compounds at 0-25 °C. In contrast, trimethyloxosulfonium ylide Me2S(O)=CH2 reacts at 50 °C, where it acts as a nucleophile initially, and an epoxide is formed from a backside attack of an oxido anion on the β-carbon. Pentacoordinate 1,2λ4-oxathietanes have been reported as intermediates in the addition step of this reaction. Different mechanisms have been proposed for this epoxidation, including the concerted mechanism, anti-addition, and torsional rotation pathways. However, trans epoxides are formed via the anti-addition pathway as the concerted mechanism is not favorable. The reaction has been modified to start with a dry mixture of trimethylsulfonium salt with potassium tert-butoxide and NaH, which remain stable, and the ylide is generated upon the addition of DMSO or a DMSO/THF solution of carbonyl compounds. Similar to the Wittig reaction, the Corey-Chaykovsky ylide leads to the formation of olefin, as shown by the reaction with benzophenone at 75-100 °C. The ylide can also add to alkene to form cyclopropane, imines to give aziridines, etc. This reaction has been made catalytically in two phases. Optical active epoxides can be obtained from the achiral aldehydes and ketones by using chiral sulfur ylides. Different chiral sulfur ylides have been designed so far.

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