Asymmetric Organocatalytic Epoxidation of α,β-Unsaturated Aldehydes

Key words

epoxidation - hydrogen peroxide - prolines

Significance

Epoxidation has long been an important synthetic transformation in synthetic chemistry. This represents the first direct formation of α,β-epoxy aldehydes which, importantly, was achieved under simple and mild conditions. Hydrogen peroxide was found to be the oxidant of choice while t-BuOOH, cumene hydroperoxide, and urea hydrogen peroxide gave similar results, but m-CPBA gave almost no conversion (< 3%).

Comment

The proposed mechanism involved formation of the imminium ion, which is nucleophilically attacked by the peroxide in 1,4-fashion. The subsequent enamine attacks the electrophilic peroxide oxygen forming the α,β-epoxy aldehyde. This type of activation of α,β-unsaturated carbonyls prompts for promising future studies for asymmetric 1,4-additions (see also: Angew. Chem. Int. Ed. 2005, 44, 3703-3706).