Brønsted Acid-Catalysed Hydroarylation of Unactivated Alkynes in Fluoroalcohol–Hydrocarbon Biphasic System: Construction of Phenanthrene Frameworks

Transition metal-free hydroarylation of unactivated alkynes was achieved by combining a Bronsted acid catalyst and a two-phase solvent system consisting of 1,1,1,3,3,3-hexafluoropropan-2-ol (HFIP) and cyclohexane. This protocol is applicable to a wide variety of 2-alkynylbiaryls which leads to the synthesis of substituted phenanthrenesvia 6-endo-selective ring closure. The biphasic system achieves highly efficient ring closure by appropriate separation of cationic intermediates from neutral compounds. The vinyl carbocationintermediates are stabilised in the HFIP phase, while the substrates and products are distributed in the cyclohexanephase to suppress intermolecular side reactions.