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 trifluoro-acetic 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 O-2 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 Bronsted acid sites in P-SiO2 that dehydrate furan-ethylene cycloadducts without substantial formation of carbon deposits.

Automated summary

4,4'-Dimethylbiphenyl (DMBP) is successfully synthesized from 2-methylfuran (MF) through a two-step process, with the intermediate 5,5'-dimethyl-2,2'-bifuran (DMBF) being crucial. The optimized reaction conditions, including high O-2 pressure and trifluoro-acetic acid concentration, significantly enhance the DMBF formation rate. The use of phosphoric acid supported on silica (P-SiO2) as the catalyst leads to high yield and selectivity in the conversion of DMBF to DMBP.