New systems for heterogeneous catalytic epoxidation

Epoxides are very useful key intermediates in the construction of synthetically challenging molecules. Owing to their strategic importance in organic synthesis, novel polymer-supported iminium salts were investigated for the catalytic oxidation of unfunctionalised alkenes. A solid-phase methodology was initiated and then developed for the evaluation of several heterogeneous catalysts. In an initial approach, immobilised iminium salts were prepared by condensation of 2-(bromoethyl)benzaldehyde with commercially available aminomethyl resins. These materials were shown to be able to successfully catalyse the epoxidation of 1-phenylcyclohexene. The epoxidation reactions were performed in a triphasic system using Oxone® as the oxidising agent and 25 mol% of the catalyst. For all the resin type employed, namely NovaSyn TG, NovaGel, ArgoGel or PEGA, complete conversion of the alkenes to their respective epoxides was obtained. [Continues.]