Unique reactivity of α,β-unsaturated carboxylic acid imidazolides: Catalytic asymmetric synthesis of α,β-epoxy esters and α,β-epoxy carboxylic acid derivatives

Catalytic asymmetric synthesis of α,β-epoxy esters and α,β-epoxy carboxylic acid derivatives is described. Catalytic asymmetric epoxidation of α,β-unsaturated carboxylic acid imidazolides using La-BINOL-Ph₃As=O complex gave the corresponding α,β-epoxy peroxy tert-butyl esters, which were directly converted to the α,β-epoxy methyl esters by adding methanol to the reaction. This catalytic system had broad generality for epoxidation of various substrates. With the use of 5-10 mol% of the catalyst, both β-aryl and β-alkyl-substituted-α,β-epoxy methyl esters were obtained in up to 91% yield and in up to 93% enantiomeric excess. In addition, efficient transformations of α,β-epoxy peroxy tert-butyl esters into the α,β-epoxy amides, α,β-epoxy aldehydes, and γ,δ-epoxy β-keto esters are also reported.