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Production of p-xylene (PX) via a broad biomass-derived furan cycloaddition has received incremental interest because of its renewable character. To date, the [4 + 2] cycloaddition reaction of furan derivatives with acrylic acid (AA) to synthesize PX has been achieved mainly by thermo-catalysis, but the stern reaction conditions usually lead to high energy costs. Herein, we report a copper-mediated decarboxylative cycloaddition within PW@HKUST-1 under visible-light irradiation to realize rapid synthesis of PX with 92.6% yield in 3 h under atmospheric pressure. Preliminary mechanistic studies reveal a radical decarboxylation process via ligand-to-metal charge transfer (LMCT) that initiates the [4 + 2] cycloaddition under visible-light irradiation. This work suggests that photoexcited [4 + 2] cycloaddition could be a cost-effective strategy for the synthesis of biomass-derived PX. [ABSTRACT FROM AUTHOR]

The construction of aromatic skeleton structures by the Diels–Alder reaction is a synthetic route to obtain substitutes for petrochemical products using biomass as a raw material. In this work, a class of SiW@MIL-100(Fe)-n (n = 1–4) catalysts containing silicotungstic acid (SiW) encaged in MIL-100(Fe) was synthesized for the mimic synthesis of p-xylene (PX). SiW@MIL-100(Fe)-3 was applied to catalyze the reaction of 2,5-dimethylfuran and acrylic acid (AA) to give aromatic products (yield 94%, PX yield = 80.1%) at 140 °C under ambient pressure. The synergistic effect between the metal centers and Lewis/Brønsted acid was increased due to the confinement effect in the cage of MIL-100(Fe). The Fe(III) sites catalyzed the decarboxylation of AA via a free radical process, avoiding the formation of the 2,5-dimethylbenzoic acid intermediate. Two types of acid sites along with the reactants as well as the reversibly adsorbed water promoted the formation of hydrogen bonds with protons from SiW, which accelerated the dehydration reaction. This strategy provides a route for the construction of aromatic skeletons from biomass derivatives by MOF-based solid acid catalysts. [ABSTRACT FROM AUTHOR]