Hypervalent-Iodine-Mediated Formation of Epoxides from Carbon(sp2)-Carbon(sp3) Single Bonds.

We have developed an efficient method for direct formation of epoxide groups from carbon(sp2)-carbon(sp3) single bonds of ß-keto esters; the reaction is mediated by the water-soluble hypervalent iodine(V) reagent AIBX (5-trimethylammonio-1,3-dioxo-1,3-dihydro-1λ5-benzo[d][1,2]iodoxol-1-ol anion). On the basis of the results of density functional theory calculations and experimental studies, we propose that the reaction proceeds by a two-stage mechanism involving dehydrogenation of the ß-keto ester substrates and epoxidation of the resulting enone intermediates. The rate-limiting step is abstraction of the ß'-C-H (calculated free energy of activation, 24.5 kcal/mol).