An innovative catalytic pathway for the synthesis of acyl furans: the cross-ketonization of methyl 2-furoate with carboxylic acids

The usefulness of ketonization reactions for the valorization of a wide plethora of biomass-derived carboxylic acids is widely recognized; however, the full potential of this reaction has yet to be suitably exploited for the production of high added-value aromatic and/or aliphatic asymmetric ketones. For this reason, herein we report for the first time in the literature the continuous-flow, gas-phase synthesis of 2-acetyl furan (AF) by means of the catalytic cross-ketonization of bio-based 2-methyl furoate (2-MF) and acetic acid (AA) over a simple and cheap ZrO2 catalyst. Interestingly, AF is considered a valuable food additive and a pharmaceutical intermediate for the synthesis of antibiotics. The optimization of the molar ratio between reactants at 350 °C allowed us to achieve 87% AF selectivity at 90% 2-MF conversion, with a space-time yield of 0.152 h−1, a value that is similar to the ones obtained by following the traditional Friedel-Crafts acylation and Wacker oxidation routes. On the other hand, the E-factor of the herein-proposed process is several times lower compared to the aforementioned traditional routes performed in the liquid phase and under batch conditions. Finally, the versatility of the cross-ketonization synthetic approach was successfully demonstrated and applied for the selective synthesis of other valuable acyl furans (i.e., propionyl furan and butyryl furan).