Regulating the Acidity of HF/Pyridine Media to Control the Chemodivergent Fluoro- and Hydro-Heteroalkylation of Olefins

Oxocarbenium ions are important reactive intermediates with many applications in organic synthesis. Among them, primary oxocarbenium ions have been much less explored, in part due to the difficulty of controlling their reactivity under standard conditions. Here, we show that the reactivity of such species can be finely modulated in strongly acidic HF/pyridine media. By leveraging the tunable acidity of HF/pyridine solutions, their reaction with olefins can be diverted toward either fluoro- or hydro-oxyalkylation. Additional spectroscopic and computational investigations provide insights into the mechanism.