eFluorination of Activated Alcohols Using Collidinium Tetrafluoroborate

Electrochemical Formation of Oxazolines by 1,3-Oxyfluorination of Non-activated Cyclopropanes

The C-C bond in non-activated cyclopropanes can be intramolecularly cleaved with an electrochemically generated amidyl radical forming oxazolines. In the presence of TBABF4, this provides 1,3-oxyfluorination products. C-C bond cleavage of cyclopropane proceeds with inversion of the configuration, suggesting an intramolecular homolytic substitution (SHi) mechanism. The performance of TBABF4 as an efficient fluoride source was explained by accumulation of the BF4- anion at the anode surface, at which a carbocation is formed by the oxidation of the C-centered radical.

Pulsed electrolysis: enhancing primary benzylic C(sp3)-H nucleophilic fluorination

Electrosynthesis is an efficient and powerful tool for the generation of elusive reactive intermediates. The application of alternative electrolysis waveforms provides a new level of control for dynamic redox environments. Herein, we demonstrate that pulsed electrolysis provides a favourable environment for the generation and fluorination of highly unstable primary benzylic cations from C(sp3)-H bonds. By introduction of a toff period, we propose this waveform modulates the electrical double layer to improve mass transport and limit over-oxidation.

Synthesis of Tertiary Fluorides through an Acid-Mediated Deoxyfluorination of Tertiary Alcohols

The combination of methanesulfonic acid and potassium bifluoride is reported for the deoxyfluorination of tertiary alcohols. Under metal-free conditions that use readily available, cheap, and easy-to-handle reagents, a range of tertiary alcohols could be converted into the corresponding fluorides in excellent yields (average yields of 85% for 23 examples). Mechanistic investigation showed that the reaction proceeds at 0 °C, in part, through an elimination/hydrofluorination pathway, but no residual alkenes are observed. The application of these conditions for the fluorination of ether and ester is also demonstrated.