A Sequential Catalytic Carbonation-Hydrolysis-Diol Dehydrogenation Reaction of Epoxides.

The design of cascade reactions in synthetic programs is of interest, particularly if the individual steps involve catalyzed reactions, and simple and highly available molecules such as carbon dioxide (CO₂), water (H₂O), and dihydrogen (H₂) are employed. Herein, a three-step sequential reaction is shown from epoxides to dehydrogenated diols, catalyzed by a combination of commercially available ionic liquids and supported Pt species on charcoal (Pt/C) in low amounts (<0.05 mol%). The process involves first carbonation of epoxides with CO₂, followed by the opening of the carbonate with H₂O, and then an acceptor-less dehydrogenation reaction of the resulting diol to release H₂. The inclusion of this last step in the one-pot synthesis of diols from epoxides is, to the knowledge, unprecedented. Reactive and kinetic experiments for each individual step reveal the key role of CO₂ to avoid epoxide polymerizations and enable the synthesis of a clean diol for the final dehydrogenation reaction.