A General Hydrotrifluoromethylation of Unactivated Olefins Enabled by Voltage‐Gated Electrosynthesis

Abstract

Here we present the first successful hydrotrifluoromethylation of unactivated olefins under electrochemical conditions. Commercially available trifluoromethyl thianthrenium salt (TT+‐CF3BF4‐, Ep/2 = –0.85 V vs Fc/Fc+) undergoes electrochemical reduction to generate CF3 radicals which add to olefins with exclusive chemoselectivity. The resulting carbon centered radical undergoes a second cathodic reduction, instead of a classical HAT process, to generate a carbanion that can be terminated by protonation from solvent. The use of MgBr2 (+0.20 V onset oxidation potential) plays a key role as an enabling sacrificial reductant for the reaction to operate in an undivided cell. Guided by cyclic voltammetry (CV) studies, fine‐tuning the solvent system, trifluoromethylating reagent’s counteranion and careful selection of redox processes, this work led to the development of a voltage‐gated electrosynthesis by pairing two redox processes with a narrow potential difference (ΔE ≈ 1.00 V) allowing the reaction to proceed with two important advances: (a) high reactivity and selectivity towards hydrotrifluoromethylation over undesired dibromination, and (b) an unprecedented functional group tolerance, including aniline, phenols, unprotected alcohol, epoxide, trialkyl amine, and several redox sensitive heterocycles.