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(sp(2))carbon(sp(3)) single bonds of beta-keto esters; the reaction is mediated by the water-soluble hypervalent iodine(V) reagent AIBX (5-trimethylammonio-1,3-dioxo-1,3-dihydro-1 lambda(5)-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 beta-keto ester substrates and epoxidation of the resulting enone intermediates. The rate-limiting step is abstraction of the beta'-CH (calculated free energy of activation, 24.5 kcal/mol).