Flavinium and Alkali‐Metal Assembly on Sulfated Chitin: A Heterogeneous Supramolecular Catalyst for H2O2‐Mediated Oxidation

Heterogeneous multiple‐catalyst assemblies were developed in which the flavinium cation and Na or Li cations were easily immobilized on a chitin‐derived anionic polymeric scaffold through noncovalent ionic interactions. The supramolecular flavinium catalysts were successfully employed in the environmentally friendly heterogeneous Baeyer–Villiger oxidation and sulfoxidation by H2O2. Owing to the cooperative catalytic effect of flavinium, alkali metal, and sulfated chitin, the supramolecular flavinium assembly showed higher catalytic activity for the Baeyer–Villiger oxidation of cyclic ketones than the corresponding homogeneous flavinium catalyst. Because the ionic assembly was stable under the reaction conditions, the catalyst could be readily recovered by simple filtration and reused.