Renewable Cyclobutane-1,3-dicarboxylic Acid (CBDA) Building Block Synthesized from Furfural via Photocyclization

Abstract

A novel renewable building block with a semirigid structure, (1α,2α,3β,4β)-2,4-di­(furan-2-yl)­cyclobutane-1,3-dicarboxylic acid (CBDA-5), was synthesized from furfural. The synthesis started with a Knoevenagel condensation between furfural and malonic acid, and a subsequent decarboxylation in the same pot, which produced 2-furanacrylic acid. The corresponding ester, ethyl-2-furanacrylate, was prepared by the Fisher or Steglich esterification of 2-furanacrylic acid with ethanol. Solvent-free [2 + 2] photodimerization of crystalline ethyl 2-furanacrylate was then carried out at −20 °C under blacklight to give diethyl 2,4-di­(furan-2-yl)­cyclobutane-1,3-dicarboxylate (CBDE-5). Afterward, CBDE-5 was hydrolyzed to give the corresponding dicarboxylic acid, CBDA-5. Both CBDE-5 and CBDA-5 were confirmed by NMR spectroscopy, Fourier transform infrared (FT-IR) spectroscopy, high-resolution mass spectrometry (HRMS), and single-crystal X-ray diffraction (XRD). A preliminary study showed that CBDE-5 and CBDA-5 could be used as renewable building blocks to produce fully biobased polyesters. In this study, several “green” techniques were applied to prepare renewable building blocks, including solvent-free crystallization, solvent- and metal-free photodimerization, and the use of residential blacklight as an energy-efficient, cost-effective, and operator-friendly UV (ECO-UV) irradiation source in the stereoregular photocycloaddition.

Terephthalic Acid Copolyesters Containing Tetramethylcyclobutanediol for High‐Performance Plastics

“… [59] On the other hand, 2,4‐diphenylcyclobutane‐1,3‐dicarboxylic acid (Ph 2 CBDA) could be esterified with linear diols like EG and PDO, but the resulting polyesters had T g of only 81 and 64 °C, respectively. [60] Nevertheless, these cyclization reactions based on biomass‐derived intermediates like cinnamic acid and furfual [61] can be beneficial for making greener polyesters.…”

Furan Polymers: State of the Art and Perspectives

“…[48] The revival here of the use of photoactive furan moieties, first exemplified by the crosslinkable copolyester depicted in Scheme 19, [31] has now been revisited, based on previous work on the photochemistry of furanacrylic structures, [49] by a report on the synthesis of a cyclobutane diacid and its ethyl ester, which were used in conjunction of ethylene glycol, for the synthesis of novel furan polyesters, as shown in Scheme 30. [50]…”

Diverse Applications of Biomass‐Derived 5‐Hydroxymethylfurfural and Derivatives as Renewable Starting Materials

“…[85] As shown in Scheme 25, CBDA-2 can be synthesized from furfural (66) by the conversion to trans-3-(2-furyl)acrylic acid (82) using a Knoevenagel condensation with malonic acid under basic conditions. Furyl acrylic acid can then be converted to CBDA-2 stereospecifically with a solidstate [2 + 2] photocycloaddition, [86] or via a similar photocycloaddition with intermediate esterification and saponification steps, [87] ostensibly for easier purification. For GQD formation, a solution of CBDA-2 was then autoclaved for 12 h at 200 °C.…”