Catalytic Asymmetric Darzens Reactions

Optically active α,β-epoxy derivatives can be converted into many types of useful chiral compounds, such as chiral building blocks and synthetic intermediates for biologically active compounds. The most up-to-date and most economical method for the preparation of enantiomeric pure epoxides is the catalytic asymmetric Darzens condensation. The homogeneous phase and heterogeneus phase (phase-transfer [PT]) catalytic methods for the synthesis of chiral α,β-epoxycarbonyl, epoxysulfonyl and epoxy-amide compounds are reviewed. The effect of chiral catalysts on the yields and enantioselectivities of the epoxides was studied in homogeneous phase and under PT conditions. The use of the most important chiral PT catalysts (ephedrinium salts, cinchona-derived salts and chiral crown ethers) in Darzens condensation is also summarized. In some cases, the relationship between the structure of catalyst and its activity is also studied.