Hydroarylation of Alkenes by Protonation/Friedel-Crafts Trapping: HFIP-Mediated Access to Per-aryl Quaternary Stereocenters.

Upon treatment with a combination of HFIP and an organic sulfonic acid, alkenes behave as Brønsted bases and protonate to give carbocations which can be trapped by electron-rich arenes. The reaction constitutes a Friedel-Crafts hydroarylation which proceeds with Markovnikov selectivity and is orthogonal to traditional metal-catalyzed processes. Intermolecular transfer hydrogenation and hydrothiolation under analogous conditions are also demonstrated.