Sn-zeolite beta as a heterogeneous chemoselective catalyst for Baeyer-Villiger oxidations

The Baeyer-Villiger oxidation, first reported more than 100 years ago(1), h as evolved into a versatile reaction widely used(2) to convert ketones-read ily available building blocks in organic chemistry-into more complex and va luable esters and lactones. Catalytic versions of the Baeyer-Villiger oxida tion are particularly attractive for practical applications, because cataly tic transformations simplify processing conditions while minimizing reactan t use as well as waste production. Further benefits are expected from repla cing peracids, the traditionally used oxidant, by cheaper and less pollutin g hydrogen peroxide(3). Dissolved platinum complexes(4) and solid acids, su ch as zeolites(5,6) or sulphonated resins(7), efficiently activate ketone o xidation by hydrogen peroxide. But these catalysts lack sufficient selectiv ity for the desired product if the starting material contains functional gr oups other than the ketone group; they perform especially poorly in the pre sence of carbon-carbon double bonds. Here we show that upon incorporation o f 1.6 weight per cent tin into its framework, zeolite beta acts as an effic ient and stable heterogeneous catalyst for the Baeyer-Villiger oxidation of saturated as well as unsaturated ketones by hydrogen peroxide, with the de sired lactones forming more than 98% of the reaction products. We ascribe t his high selectivity to direct activation of the ketone group, whereas othe r catalysts first activate hydrogen peroxide, which can then interact with the ketone group as well as other functional groups.