Selective Synthesis of 4,4′-Dimethylbiphenyl from 2‑Methylfuran

4,4′-Dimethylbiphenyl (DMBP) is a promising platform chemical for the production of polymer precursors, plasticizers, and metal–organic frameworks among other materials. We report a two-step process to produce DMBP from 2-methylfuran (MF) via the formation of the intermediate 5,5′-dimethyl-2,2′-bifuran (DMBF). DMBF is generated from the Pd-catalyzed oxidative coupling of MF in the presence of trifluoroacetic acid (TFA) with high selectivity (94%). Optimization of reaction conditions yields a 20-fold increase in site-time-yield (STY = 6.99 h^–1) compared with a previously reported protocol. High O₂ pressure (7 bar) and a high TFA concentration (3 M) are critical to improve the DMBF formation rate. For the conversion of DMBF to DMBP, we show that phosphoric acid supported on silica (P-SiO₂) catalyzes tandem Diels–Alder and dehydration reactions of DMBF with ethylene to produce DMBP (83% yield). The high yield and selectivity are a consequence of the weak Brønsted acid sites in P-SiO₂ that dehydrate furan-ethylene cycloadducts without substantial formation of carbon deposits.