Furfural-Derived Diacid Prepared by Photoreaction for Sustainable Materials Synthesis

A cis-3,4-di­(furan-2-yl)­cyclobutane-1,2-dicarboxylic acid (CBDA-2) is readily prepared stereospecifically from trans-3-(2-furyl)­acrylic acid, a furfural-derived compound, through a solid-state [2 + 2] photocycloaddition in 95% isolated yield. The cyclobutane ring in CBDA-2 shows desired stabilities during thermal, sunlight, and chemical tests. The single crystal structure of CBDA-2 revealed the geometry of this molecule and orientation of the two dicarboxylic acid groups displaying its potential to serve as a unique, semirigid diacid building block in material science. A preliminary study showed that condensation of this diacid with glycerol yielded a green polymer with good stability. The diacid could also be used as a cross-linker for a biobased epoxy to yield an exceptionally hard and solvent-resistant thermoset.