‘Metal Ion Electrophilic Catalysis’ in Ring-Opening Reactions of 1,2-Epoxides by Metal Halides in Ionic Liquids

Metal ion electrophilic catalysis (Li+ > Na+ >> K+) has been found in ring-opening reactions of 1,2-epoxides 1-5 by metal halides MHal in ionic liquids. The results have been rationalized on the basis of a transition state where the cation M+ stabilizes the ­negative charge developing on the oxygen atom of the oxirane ring while favoring the nucleophilic attack at the adjacent carbon by the ion-paired anion Hal-.