Green Syntheses of Heterocycles of Industrial Importance. 5-Hydroxymethylfurfural as a Platform Chemical

Abstract The dwindling supply of fossil resources makes it interesting to find renewable resources for our everyday chemicals. 5-Hydroxymethylfurfural (HMF) is easily produced from fructose, although its isolation is not easy in view of its poor stability. More stable equivalents are its ethers or esters or 5-chloromethylfurfural. In this review, we discuss all products that have been made from HMF in the period 2013–2016. Practically in all transformations, catalysis played a major role. One major product obtained by catalyzed oxidation of HMF is 2,5-furandicarboxylic acid, that is touted as a replacement of phthalic acid in polymers. Other compounds that have been made from HMF via hydrogenation and that could find use as monomers are 2,5-furandimethanol, 2,5-tetrahydrofurandimethanol, 1,2,6-hexanetriol, 1,6-hexanediol, 5-hydroxymethyl-2-furanoic acid, and 2,5-diaminomethylfuran. Another interesting oxidation product is 2,5-diformylfuran. Also the nylon intermediates caprolactam, adipic acid, and hexamethylenediamine have been made from HMF. Hydrogenation of HMF in water under slightly acidic conditions gives 1-hydroxy-2,5-hexanedione, which can be cyclized to a cyclopentenone derivative. Acyloin condensation gives the dimeric product, which can be hydrogenated to a diesel fuel substitute. Carbon–carbon bond formation has been performed both by Diels–Alder reaction on the furan as well as by condensation on the aldehyde and/or alcohol functionalities. Hydrogenolysis of the side chains leads to formation of 2,5-dimethylfuran, which has been proposed as fuel additive. Oxidation of HMF to butenolides, maleic acid, and anhydride as well as succinic acid has been reported. Various other transformations are also described. It is expected that HMF will be increasingly important in the direct future and, indeed, commercial production of HMF and some of its derivatives has already commenced.