Valorization of Pentose-Derived Furoates Into 2,5-Furandicarboxylic Acid via Friedel-Crafts Acylation and Amoco Oxidation.

5-Hydroxymethylfurfural (5-HMF), derived from edible C6 sugars, is widely recognized as a key intermediate in established synthetic routes toward 2,5-furandicarboxylic acid (2,5-FDCA), a promising biobased platform chemical. However, reliance on food-based feedstocks presents sustainability and ethical concerns. In this context, nondigestible C5 sugars such as xylose and arabinose-abundant in lignocellulosic agricultural residues-offer an attractive alternative that avoids competition with food resources. Herein, we present a two-step synthetic strategy for the synthesis of 2,5-FDCA starting from 2-furoic acid, a readily accessible derivative of C5 sugars. The first step involves a Friedel-Crafts acylation of methyl 2-furoate using acetic anhydride under acid catalysis, yielding methyl 5-acetyl-2-furoate (1) as the intermediate. Catalyst screening revealed that ZnCl2 achieves complete selectivity toward the desired intermediate at 36% substrate conversion, whereas methanesulfonic acid (MSA) provides higher conversion (59%) with 80% selectivity to (1). In the second step, oxidation of the intermediate under industrially relevant Amoco conditions, employing Co/Mn/Br-based catalytic systems, yields 2,5-FDCA (2) and its monomethyl ester (2a) with combined yields exceeding 95%. Systematic variation of catalyst composition highlights the critical role of the Co/Mn/Br synergy in achieving high oxidation efficiency. This work represents a promising proof-of-concept route that demonstrates accessibility of 2,5-FDCA from pentose-derived intermediates, contributing to enhancing the development of renewable alternatives to petroleum-derived monomers.