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.