Mechanism of the MeReO3-Catalyzed Deoxygenation of Epoxides

The reaction mechanisms for the MTO-catalyzed deoxygenation of epoxides and diols were investigated with the aid of density functional theory (DFT) calculations. The DFT results indicate that the reaction starts with a [2 sigma-2 pi] addition of epoxide to MTO to give a five-membered-ring rhena-2,5-dioxolane intermediate, followed by H-2 addition, proton transfer, and extrusion of olefin to regenerate the catalyst. The experimental observation for formation and subsequent disappearance of diol appearing in the catalytic reaction is explained as follows. Diol was produced by the hydrolysis of epoxide with the coproduct water through the five-membered-ring rhena-2,5-dioxolane intermediate. Then the diol produced undergoes catalytic conversion to olefin by reacting with H-2 under the catalytic conditions