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.