An activated manganese dioxide (MnO₂)–BF₃·OEt₂ oxidation system was developed to efficiently mediate the intramolecular as well as intermolecular biaryl coupling. The oxidative coupling proceeds smoothly at ambient temperature to deliver the corresponding five- to eight-membered tricyclic products in good to excellent yields. The employment of the combination of MnO₂ and BF₃·OEt₂ is attractive on the basis of economical and environmental issues.