page_title: Juliá–Colonna epoxidation
section_title: Reaction mechanism
hierarchical_section_title: Juliá–Colonna epoxidation / Reaction mechanism
caption_attribution_description: English: The generic mechanism for nucleophilic epoxidation of an electron-deficient olefin indicates that the reaction proceeds through a resonance stabilized peroxide enolate intermediate.
context_page_description: The Juliá–Colonna epoxidation is an asymmetric poly-leucine catalyzed nucleophilic epoxidation of electron deficient olefins in a triphasic system. The reaction was reported by Sebastian Juliá at the Chemical Institute of Sarriá in 1980, with further elaboration by both Juliá and Stefano Colonna.
  In the original triphasic protocol, the chalcone substrate is soluble in the organic phase, generally toluene or carbon tetrachloride. The alkaline hydrogen peroxide oxidant is soluble primarily in the aqueous phase, and the reaction occurs at the insoluble polymer layer at the interface of the two phases. Alternative biphasic and monophasic protocols have been developed with increased substrate accessibility and reaction rate.
  The efficient enantioselective catalytic epoxidation under mild conditions is of great synthetic utility. Not only are epoxides effective synthons for a range of transformations, they have a significant presence in natural products structures. Furthermore, the reaction has been effectively scaled up to industrially useful levels, with work conducted notably by Bayer and Evonik.
context_section_description: The Juliá–Colonna epoxidation is an asymmetric nucleophilic epoxidation of electron-deficient olefins such as α,β-unsaturated ketones. The general mechanism shown in Figure 2 applies to all nucleophilic epoxidations but is controlled in this reaction by the poly-leucine catalyst.
  The hydroperoxide anion and chalcone assemble in a complex with the poly-leucine catalyst before reacting to form a peroxide enolate intermediate. The intermediate subsequently closes, as controlled by the catalyst structure, to form the epoxide product stereoselectively.
caption: Figure 2: The generic mechanism for nucleophilic epoxidation of an electron-deficient olefin indicates that the reaction proceeds through a resonance stabilized peroxide enolate intermediate.
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