Furylated flavonoids: fully biobased building blocks produced by condensed tannins depolymerization

An original method has been set up to produce fully biobased phenolic building blocks from condensed tannins, largely available from agroindustrial residues or wood industry coproducts. The acid-catalyzed depolymerization of condensed tannins in the presence of furan or sylvan in mild conditions (30–40 °C, 0.1 M HCl) gives the corresponding furylated flavonoids with high yields. The reaction was more efficient with sylvan than with the less nucleophilic furan. A key feature of the products is the high stability of the flavanyl to furyl C–C linkage compared to the thioether bond obtained by the classical thiolysis, which makes them promising platform molecules for further functionalization, including in alkaline conditions. The simplicity of the process makes it easy to scale-up, and the reaction can be carried out on raw plant materials directly. In accordance with green chemistry concepts, solvents and excess reagents can readily be recovered by distillation and recycled.