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.

中文翻译：

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由2-甲基呋喃选择性合成4,4'-二甲基联苯

4,4'-二甲基联苯（DMBP）是一种有前途的平台化学品，可用于生产聚合物前体，增塑剂以及其他材料中的金属有机骨架。我们报告了通过中间5,5'-二甲基-2,2'-联呋喃（DMBF）的形成，由2-甲基呋喃（MF）生产DMBP的两步过程。DMBF是在三氟乙酸（TFA）存在下，由Pd催化的MF的氧化催化偶联生成的，具有高选择性（94％）。与先前报道的方案相比，优化反应条件可将站点时间产量提高20倍（STY = 6.99 h ^–1）。高氧₂压力（7 bar）和高TFA浓度（3 M）对于提高DMBF形成速率至关重要。对于DMBF到DMBP的转化，我们表明负载在二氧化硅上的磷酸（P-SiO ₂）催化串联Diels-Alder以及DMBF与乙烯的脱水反应，生成DMBP（83％收率）。高收率和选择性是P-SiO ₂中弱的布朗斯台德酸位的结果，该位点使呋喃-乙烯环加合物脱水而基本不形成碳沉积物。