Direct, Catalytic Monofluorination of sp³ C–H Bonds: A Radical-Based Mechanism with Ionic Selectivity

Recently, our group unveiled a system in which an unusual interplay between copper­(I) and Selectfluor effects mild, catalytic sp3 C–H fluorination. Herein, we report a detailed reaction mechanism based on exhaustive EPR, 19F NMR, UV–vis, electrochemical, kinetic, synthetic, and computational studies that, to our surprise, was revealed to be a radical chain mechanism in which copper acts as an initiator. Furthermore, we offer an explanation for the notable but curious preference for monofluorination by ascribing an ionic character to the transition state.