Directing-Group-Free, Carbonyl Group-Promoted Catalytic C-H Arylation of Bio-Based Furans

An efficient strategy was developed for directing-group-free C–H functionalization of biomass-derived C6 furanic building block. Palladium-catalyzed C–H functionalization of the low-reactive C3 position was successfully performed in 2,5-diformylfuran, an important derivative of the biobased platform chemical 5-(hydroxymethyl)furfural. The ligand-free catalytic arylation was carried out without using protecting or directing groups, which is of key importance for the studied area to achieve waste-minimized and step-economic biomass processing. The experimental results combined with density functional theory calculations revealed a reaction mechanism and indicated that the presence of the aldehyde group is essential for catalytic reaction. Enolization of the aldehyde group and Pd binding play an important role in governing the overall C–H functionalization pathway. One of the obtained arylated furanic compounds was tested as a model substrate for reduction and oxidation of carbonyl groups to highlight its versatile synthetic potential.