Multifunctional catalysis promoted by solvent effects: Ti-mcm41 for a one-pot, four-step, epoxidation-rearrangement-oxidation-decarboxylation reaction sequence on stilbenes and styrenes

Titanium sites grafted on several siliceous supports are able to act as multifunctional catalytic centers, activating tert-butyl hydroperoxide for oxidation reactions, as redox centers, and promoting rearrangements, as Lewis acids. In the one-pot, four-step conversion of stilbene into benzophenone, the best results were obtained over Ti-MCM41. Under suitable conditions, the catalyst promotes a tandem sequence: alkene epoxidation, epoxide rearrangement, aldehyde oxidation, and oxidative decarboxylation. ?,?,?-Trifluorotoluene and a fluorinated glycerol-derived solvent were the optimal solvents for this tandem process, due to their polar aprotic character that allows the efficient oxidation reactions and a poor coordinating ability to prevent any deactivation of the Lewis acid character of the sites. The result of the tandem sequence of reactions is a ketone with loss of a carbon atom that, depending on the starting alkene, is the same result as that of an ozonolysis but under safer and milder conditions. Interesting and new insights on the mechanism of the different reactions involved are also described.